Electronic device

ABSTRACT

An easy to use electronic device is provided. The electronic device functions as a telephone and has a display portion, an audio input portion, an audio output portion, and operation keys. The display portion has a passive element, and the operation keys have LEDs. The direction of an image displayed by the LEDs is switchable.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an electronic device functioningas a telephone machine (telephone), and particularly to a portableinformation terminal. The present invention relates in particular to aportable information terminal having EL elements in a display portion.Note that, in this specification, a portable information terminaldenotes a communication device capable of being carried by a user andwhich possesses both a function of being able to exchange data withanother individual while in motion, and a function as a telephone.

[0003] 2. Description of the Related Art

[0004] Technology relating to flat panel displays has been developingrapidly in recent years under the background of increasing needs forlighter, thinner, and smaller displays. Flat panel displays are capableof displaying an image which is high quality, full color, and has highresolution. One type of flat panel display, liquid crystal displaydevices, are used in display portions of portable information terminals(such as a mobile computer, a portable telephone, a portable type gamemachine, and an electronic book).

[0005]FIG. 25 shows a portable telephone, which is one type of portableinformation terminal having a liquid crystal display device. Theportable telephone shown in FIG. 25 includes a main body 2801, an audiooutput portion 2802, an audio input portion 2803, a display portion2804, operation keys 2805, and an antenna 2806.

[0006] The portable telephone shown in FIG. 25 has a function as atelephone, namely it converts audio input to the audio input portion2803 into electric waves and then outputs the electric waves, and ittakes in electric waves having audio information to convert it to audio,then plays the audio in the audio output portion.

[0007] A liquid crystal display device is used in the display portion2804, and is capable of displaying necessary information.

[0008] With the conventional portable information terminal shown in FIG.25, images such as characters, numerals, or symbols are listed on ordisplayed on the operation keys so that the operator can recognize whattype of information is input to the portable information terminal whenwhich operation key is pressed. However, the direction of thecharacters, numerals, or symbols displayed on the operation keys isalways fixed with a conventional portable information terminal. Theoperator therefore must use the portable information terminal by alwaysaligning with the direction of the characters, numerals, or symbolsdisplayed on the operation key, and the portable information terminalitself is not user friendly.

SUMMARY OF THE INVENTION

[0009] In view of the above problem, an object of the present inventionis to provide a portable information terminal which is easy to use.

[0010] A portable information terminal of the present invention hasoperation keys for inputting information, each with an LED (lightemitting diode), EL display device, or liquid crystal display device,and by displaying characters, symbols, and numerals in the operationkeys in accordance with the LEDs, EL display devices, or liquid crystaldisplay devices, an operator can differentiate between the operationkeys. The operator can even discern the operation keys in a darkenvironment in accordance with the above structure.

[0011] The operator can appropriately change the direction of the imagesdisplayed in the display portion, and can appropriately change thedirection of the images such as characters, symbols, and numeralsdisplayed in the operation keys, in accordance with the portableinformation terminal usage. The ease of use of the portable informationterminal can be improved with the above structure.

[0012] Further, the portable information terminal of the presentinvention may also use a structure having a CCD camera. By using the CCDcamera, the operator can send image information, taken in as electronicdata to the portable image terminal by the CCD camera, to other personson the spot.

[0013] Structures of the present invention are shown below.

[0014] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising: a displayportion; an audio input portion; an audio output portion; and operationkeys;

[0015] characterized in that:

[0016] the display portion has active elements;

[0017] the operation keys have LEDs; and

[0018] the direction of an image displayed by the LEDs is switchable.

[0019] An electronic device may be characterized in that the activeelement has EL or liquid crystals.

[0020] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising: a displayportion; an audio input portion; an audio output portion; and operationkeys;

[0021] characterized in that:

[0022] the display portion has EL elements;

[0023] the operation keys have liquid crystals; and

[0024] the direction of an image displayed by the liquid crystals isswitchable.

[0025] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising:

[0026] a first panel having: one of an audio input portion and an audiooutput portion; and a display portion;

[0027] a second panel having: one of an audio input portion and an audiooutput portion; and operation keys;

[0028] characterized in that:

[0029] the first panel and the second panel are connected;

[0030] the angle between the first panel and the second panel can bearbitrarily changed;

[0031] the display portion has EL elements;

[0032] the operation keys have LEDs; and

[0033] the direction of an image displayed by the LEDs is switchable.

[0034] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising:

[0035] a first panel having: one of an audio input portion and an audiooutput portion; and a display portion;

[0036] a second panel having: one of an audio input portion and an audiooutput portion; and operation keys;

[0037] characterized in that:

[0038] the first panel and the second panel are connected;

[0039] the angle between the first panel and the second panel can bearbitrarily changed;

[0040] the display portion has EL elements;

[0041] the operation keys have liquid crystals; and

[0042] the direction of an image displayed by the liquid crystals isswitchable.

[0043] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising:

[0044] a first panel having: one of an audio input portion and an audiooutput portion; and a display portion;

[0045] a second panel having: one of an audio input portion and an audiooutput portion; and operation keys;

[0046] characterized in that:

[0047] the display portion has EL elements;

[0048] the operation keys have LEDs; the first panel and the secondpanel are connected;

[0049] the angle between the first panel and the second panel can bearbitrarily changed;

[0050] the direction of an image displayed by the LEDs is switchable inaccordance with the angle between the first panel and the second panel.

[0051] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising:

[0052] a first panel having: one of an audio input portion and an audiooutput portion; and a display portion;

[0053] a second panel having: one of an audio input portion and an audiooutput portion; and operation keys;

[0054] characterized in that:

[0055] the display portion has EL elements;

[0056] the operation keys have liquid crystals;

[0057] the first panel and the second panel are connected;

[0058] the angle between the first panel and the second panel can bearbitrarily changed;

[0059] the direction of an image displayed by the liquid crystals isswitchable in accordance with the angle between the first panel and thesecond panel.

[0060] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising:

[0061] a first panel having: one of an audio input portion and an audiooutput portion; and a display portion;

[0062] a second panel having: one of an audio input portion and an audiooutput portion; and operation keys;

[0063] characterized in that:

[0064] the first panel and the second panel are connected;

[0065] the angle between the first panel and the second panel can bearbitrarily changed;

[0066] the display portion has a plurality of pixels;

[0067] the plurality of pixels each have: a photodiode; an EL element; aswitching TFT; an EL driver TFT; a reset TFT; a buffer TFT; and aselection TFT;

[0068] the switching TFT and the EL driver TFT control light emissionfrom the EL element;

[0069] light emitted from the EL elements is reflected upon a subjectand irradiated onto the photodiodes;

[0070] the photodiodes, the reset TFTs, the buffer TFTs, and theselection TFTs generate an image signal from the light irradiated ontothe photodiodes;

[0071] the operation keys have LEDs; and

[0072] the direction of an image displayed by the LEDs is switchable.

[0073] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising:

[0074] a first panel having: one of an audio input portion and an audiooutput portion; and a display portion;

[0075] a second panel having: one of an audio input portion and an audiooutput portion; and operation keys;

[0076] characterized in that:

[0077] the first panel and the second panel are connected;

[0078] the angle between the first panel and the second panel can bearbitrarily changed;

[0079] the display portion has a plurality of pixels;

[0080] the plurality of pixels each have: a photodiode; an EL element; aswitching TFT; an EL driver TFT; a reset TFT; a buffer TFT; and aselection TFT;

[0081] the switching TFT and the EL driver TFT control light emissionfrom the EL element;

[0082] light emitted from the EL elements is reflected upon a subjectand irradiated onto the photodiodes;

[0083] the photodiodes, the reset TFTs, the buffer TFTs, and theselection TFTs generate an image signal from the light irradiated ontothe photodiodes;

[0084] the operation keys have liquid crystals; and

[0085] the direction of an image displayed by the liquid crystals isswitchable.

[0086] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising: a displayportion; an audio input portion; an audio output portion; and operationkeys;

[0087] characterized in that:

[0088] the display portion have first EL elements;

[0089] the operation keys have second EL element; and

[0090] the direction of an image displayed by the second EL elements isswitchable.

[0091] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising:

[0092] a first panel having: one of an audio input portion and an audiooutput portion; and a display portion;

[0093] a second panel having: one of an audio input portion and an audiooutput portion; and operation keys;

[0094] characterized in that:

[0095] the first panel and the second panel are connected;

[0096] the angle between the first panel and the second panel can bearbitrarily changed;

[0097] the display portion has first EL elements;

[0098] the operation keys have second EL elements; and

[0099] the direction of an image displayed by second EL elements isswitchable.

[0100] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising:

[0101] a first panel having: one of an audio input portion and an audiooutput portion; and a display portion;

[0102] a second panel having: one of an audio input portion and an audiooutput portion; and operation keys;

[0103] characterized in that:

[0104] the display portion has first EL elements;

[0105] the operation keys have second EL elements;

[0106] the first panel and the second panel are connected;

[0107] the angle between the first panel and the second panel can bearbitrarily changed; and

[0108] the direction of an image displayed by second EL elements isswitchable in accordance with the angle between the first panel and thesecond panel.

[0109] According to the present invention, there is provided anelectronic device functioning as a telephone, comprising:

[0110] a first panel having: one of an audio input portion and an audiooutput portion; and a display portion;

[0111] a second panel having: one of an audio input portion and an audiooutput portion; and operation keys;

[0112] characterized in that:

[0113] the first panel and the second panel are connected;

[0114] the angle between the first panel and the second panel can bearbitrarily changed;

[0115] the display portion has a plurality of pixels;

[0116] the plurality of pixels each have: a photodiode; a first ELelement; a switching TFT; an EL driver TFT; a reset TFT; a buffer TFT;and a selection TFT;

[0117] the switching TFT and the EL driver TFT control light emissionfrom the first EL element;

[0118] light emitted from the first EL elements is reflected upon asubject and irradiated onto the photodiodes;

[0119] the photodiodes, the reset TFTs, the buffer TFTs, and theselection TFTs generate an image signal from the light irradiated ontothe photodiodes;

[0120] the operation keys have second EL elements; and

[0121] the direction of an image displayed by the second EL elements isswitchable.

[0122] An electronic device may be characterized in that the first ELelements each have an anode, a cathode, and an EL layer formed betweenthe anode and the cathode; and

[0123] the external quantum efficiency of the EL layer is equal to orgreater than 10%.

[0124] An electronic device may be characterized in that the maximumvalue of the strength of light emitted by the first EL elements is equalto or greater than 251 m/W.

[0125] An electronic device may be characterized in that the second ELelements each have an anode, a cathode, and an EL layer formed betweenthe anode and the cathode; and

[0126] the external quantum efficiency of the EL layer is equal to orgreater than 10%.

[0127] An electronic device may be characterized in that the maximumvalue of the strength of light emitted by the second EL elements isequal to or greater than 251 m/W.

[0128] An electronic device may be characterized by having a CCD lightreceiving portion.

[0129] An electronic device may be characterized in that an image istaken in as electronic date in the CCD light receiving portion.

[0130] An electronic device may be characterized in that:

[0131] the display portion has a touch panel; and

[0132] an image written into the touch panel is read in as electronicdata.

BRIEF DESCRIPTION OF THE DRAWINGS

[0133] In the accompanying drawings:

[0134]FIGS. 1A and 1B are external views of a portable informationterminal of the present invention;

[0135]FIGS. 2A and 2B are blow up diagrams of an operation panel of aportable information terminal of the present invention;

[0136]FIGS. 3A and 3B are top surface diagrams of a portable informationterminal of the present invention;

[0137]FIGS. 4A and 4B are external views of a portable informationterminal of the present invention;

[0138]FIGS. 5A and 5B are a blow up diagram of operation keys and adriver circuit, respectively, of a portable information terminal of thepresent invention;

[0139]FIG. 6 is a circuit diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

[0140]FIG. 7 is a top surface diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

[0141]FIG. 8 is a timing chart showing a method of driving an EL displaydevice used in a display portion of a portable information terminal ofthe present invention;

[0142]FIG. 9 is a top surface diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

[0143]FIG. 10 is a timing chart of a method of driving an EL displaydevice used in a display portion of a portable information terminal ofthe present invention;

[0144]FIG. 11 is a top surface diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

[0145]FIG. 12 is a circuit diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

[0146]FIG. 13 is a timing chart showing a method of driving an ELdisplay device used in a display portion of a portable informationterminal of the present invention;

[0147]FIGS. 14A to 14D are diagrams showing a method of manufacturing anEL display device used in a display portion of a portable informationterminal of the present invention;

[0148]FIGS. 15A to 15C are diagrams showing the method of manufacturingthe EL display device used in the display portion of the portableinformation terminal of the present invention;

[0149]FIGS. 16A to 16C are diagrams showing the method of manufacturingthe EL display device used in the display portion of the portableinformation terminal of the present invention;

[0150]FIGS. 17A and 17B are diagrams showing the method of manufacturingthe EL display device used in the display portion of the portableinformation terminal of the present invention;

[0151]FIGS. 18A and 18B are diagrams showing a mounting position of atouch panel and a touch panel structure;

[0152]FIG. 19 is a circuit diagram of an EL display device used in adisplay portion of a portable information terminal of the presentinvention;

[0153]FIG. 20 is a circuit diagram of a pixel of an EL display deviceused in a display portion of a portable information terminal of thepresent invention;

[0154]FIGS. 21A and 21B are external diagrams of an EL display deviceused in a display portion of a portable information terminal of thepresent invention;

[0155]FIG. 22 is a cross sectional diagram of an EL display device usedin a display portion of a portable information terminal of the presentinvention;

[0156]FIGS. 23A and 23B are a top surface view and a circuit diagram,respectively, of a pixel of an EL display device used in a displayportion of a portable information terminal of the present invention;

[0157]FIG. 24 is a cross sectional diagram of an EL display device usedin a display portion of a portable information terminal of the presentinvention;

[0158]FIG. 25 is a diagram of a conventional portable telephone;

[0159]FIG. 26 is a cross sectional diagram of a passive type EL displaydevice;

[0160]FIG. 27 is a circuit diagram of a liquid crystal display device:and

[0161]FIGS. 28A to 28C are cross sectional diagrams of a connectionportion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0162] Embodiment Mode

[0163] An example of a structure of a portable information terminal ofthe present invention is shown in FIG. 1A. Reference numeral 101 denotesa display panel, and reference numeral 102 denotes an operation panel.The display panel 101 and the operation panel 102 are connected in aconnection portion 103. An angle θ between a plane in which a displayportion 104 of the display panel 101 is formed, and a plane in whichoperation keys 106 of the operation panel 102 are formed, can then bearbitrarily changed.

[0164] A structure of the portable information terminal in a state inwhich the display panel 101 and the operation panel 102 overlap is shownin FIG. 1B. In this case, the angle θ becomes 0².

[0165] The display panel 101 has the display portion 104. Further, thedisplay portion 101 has an audio output portion 105, and audio is outputfrom the audio output portion 105. The display portion 104 of theportable information terminal of the present invention is structured by:an EL display device using an active element (EL element) having a layercontaining an organic compound (hereafter referred to as organiccompound layer) in which luminescence is generated by application of anelectric field; or a liquid crystal display device using an activeelement having liquid crystals.

[0166] The EL display device is also referred to as an organic ELdisplay (OELD) and an organic light emitting diode (OLED). The ELdisplay device, differing from the liquid crystal display device, is aself light emitting type. EL elements have a structure in which a layercontaining an organic compound which generated luminescence by applyingan electric field (hereafter referred to as organic substance layer) issandwiched between a pair of electrodes (an anode and a cathode), andthe organic compound layer usually has a lamination structure. Alamination structure of a hole transporting layer, a light emittinglayer, and an electron transporting layer developed by Tang, et al., ofEastman Kodak Company can be given as a typical lamination structure.This structure has extremely high light emitting efficiency, and most ofthe EL display devices currently being researched and developed employthis structure.

[0167] Electroluminescence generated by the application of an electricfield is obtained in the EL element, which has an anode layer, anorganic compound layer, and a cathode layer. There is emission of lightin the luminescence of the organic compound when returning to a groundstate from a singlet excitation state (fluorescence), and when returningto a ground state from a triplet excitation state (phosphorescence), andthe light emitting device of the present invention may use both types oflight emission.

[0168] Further, a structure in which a hole injecting layer, a holetransporting layer, a light emitting layer, and an electron transportinglayer are laminated in order on an electrode; and a structure in which ahole injecting layer, a hole transporting layer, a light emitting layer,an electron transporting layer, and an electron injecting layer arelaminated in order on an electrode may also be used. Doping of amaterial such as a fluorescent pigment into the light emitting layer mayalso be performed.

[0169] All layers formed between one pair of electrodes are referred togenerically as organic compound layers within this specification. Theabove stated hole injecting layer, hole transporting layer, lightemitting layer, electron transporting layer, electron injecting layer,and the like are therefore all contained within the organic compoundlayer.

[0170] Elements formed by an anode, an organic compound layer, and acathode are referred to as EL elements in this specification. Theoperation panel 102 has the operation keys 106, a power source switch107, an audio input portion 108, and a CCD light receiving portion 109.Note that, although the operation keys 106 and the power source switch107 are formed separately in this embodiment mode, a structure in whichthe power source switch 107 is contained within the operation keys 106may also be used.

[0171] Audio is input in the audio input portion 107. An image input inthe CCD light receiving portion 109 is taken in as electronic data bythe portable information terminal.

[0172] Note that, although the display panel 101 has the audio outputportion 105 in FIGS. 1A and 1B, and the operation panel has the audioinput portion 108, the present invention is not limited to thisstructure. The display panel 101 may have the audio input portion 108,and the operation panel may have the audio output portion 105. Further,both the audio output portion 105 and the audio input portion 108 may beformed together in the display panel 101, and both the audio outputportion 105 and the audio input portion 108 may be formed together inthe operation panel 102.

[0173] Furthermore, the portable information terminal of the presentinvention has the operation keys 106 each having a means of display suchas an LED, a liquid crystal display device, or an EL display device.Characters, symbols, numerals, and the like are displayed in therespective operation keys 106 by the LEDs, liquid crystal displaydevices, or EL display devices of each operation key 106.

[0174] Note that the portable information terminal does not have anantenna in this embodiment mode, but an antenna may also be formed whennecessary.

[0175]FIGS. 2A and 2B show an enlarged diagram of the operation panel102. Portions which are the same as those shown in FIGS. 1A and 1B usethe same reference symbols.

[0176] The operation keys 106 shown in FIG. 2A display a single number,or a plurality of, characters, symbols, numerals, and the like in ablack color on a white color background. The operation keys 106 shown inFIG. 2B display a single number, or a plurality of, characters, symbols,numerals, and the like in a white color on a black color background.

[0177] Note that, although the operation keys performing display byblack or white colors is explained with FIG. 2A and FIG. 2B, the presentinvention is not limited to this. The operation keys may also performdisplay of a color other than white. For example, yellow color displayon a black color background, green color display on a white colorbackground, and black color display on a blue color background may alsobe performed.

[0178] Further, with the portable information terminal of the presentinvention, it is possible for an operator to suitably change thedirection of an image displayed in the display portion 104, and thedirection of images such as characters, numerals, and symbols displayedin the operation keys 106. FIGS. 3A and 3B show top surface views of aportable information terminal.

[0179]FIG. 3A shows a case of original directions seen from theoperator, for the direction of the image displayed in the displayportion 104 and the direction of the images such as characters,numerals, and symbols displayed in the operation keys 106, when thedisplay panel 101 and the operation panel 102 are placed next to eachother horizontally.

[0180]FIG. 3B shows a case of original directions seen from theoperator, for the direction of the image displayed in the displayportion 104 and the direction of the images such as characters,numerals, and symbols displayed in the operation keys 106, when thedisplay panel 101 and the operation panel 102 are placed next to eachother vertically.

[0181] With the portable information terminal of the present invention,it is possible to switch between the direction shown in FIG. 3A and thedirection shown in FIG. 3B, in accordance with the preference of theoperator regarding ease of use, for the direction of the image displayedin the display portion 104 and the direction of the images such ascharacters, numerals, and symbols displayed in the operation keys 106.

[0182] Note that, although a case in which the direction of the imagedisplayed in the display portion 104, and the direction of the imagessuch as characters, numerals, and symbols displayed in the operationkeys 106, are always the same is explained with FIGS. 2A and 2B, thepresent invention is not limited to this. The directions of the imagedisplayed in the display portion 104 and the direction of the imagessuch as characters, numerals, and symbols displayed in the operationkeys 106 may also differ.

[0183] Note that one example of images such as characters, numerals, andsymbols displayed in the operation keys is shown in FIGS. 2A and 2B, andthat the portable information terminal of the present invention is notlimited to those characters, numerals, and symbols.

[0184] Further, a structure in which the direction of the imagesdisplayed in the display portion 104 and the direction of the imagessuch as characters, numerals, and symbols displayed in the operationkeys 106 can be automatically changed in accordance with an angle θbetween a plane having the display portion 104 of the display panel 101,and a plane having the operation keys 106 of the operation panel 102, inthe connection portion 103.

[0185] For example, for a case in which the angle θ is equal to orgreater than 180, as shown in FIG. 4A, the direction of the imagedisplayed in the display portion 104 and the direction of the imagessuch as characters, numerals, and symbols displayed in the operationkeys 106 switches to the direction shown in FIG. 3A. Then, for a case inwhich the angle θ is greater than or equal to 0° and less than or equalto 180°, the direction of the image displayed in the display portion 104and the direction of the images such as characters, numerals, andsymbols displayed in the operation keys 106 switch to the directionshown in FIG. 3B.

[0186] The portable information terminal of the present invention canthus be made into a device which is easy to use for the operator inaccordance with the above structure.

[0187] Embodiments

[0188] Embodiments of the present invention are explained below.

[0189] Embodiment 1

[0190] A structure of operation keys of a portable information terminalof the present invention is explained in detail in Embodiment 1.

[0191] A blow up diagram of the operation keys of the portableinformation terminal of the present embodiment is shown in FIG. 5A. Theoperation keys of Embodiment 1 have a total of 8×8 pixels in which eightcolumns x1 to x8 and eight rows y1 to y8 are arranged in a matrix shape.Note that, although a structure having a total of 8×8 pixels is shown inEmbodiment 1, the present invention is not limited to this. The numberof pixels of the operation keys can be suitably determined by a userimplementing the present invention.

[0192]FIG. 5B shows a driver circuit group of the operation keys of theportable information terminal shown in FIG. 5A. Reference numeral 151denotes a column driver circuit, and the column driver circuit inputsdisplay data to each of the eight columns of pixels x1 to x8. Referencenumeral 152 denotes a row driver circuit, and the row driver circuitselects the eight rows y1 to y8 in order so that the display data inputto the eight columns x1 to x8 is input to designated pixels.

[0193] Each pixel of the operation keys has an LED, an EL displaydevice, or a liquid crystal display device.

[0194] The display data is stored in a first memory 153 and a secondmemory 154, respectively. By selecting one of the first memory 153 andthe second memory 154, the display data stored in the selected memory isinput to the column driver circuit 151.

[0195] The images such as characters, numerals, and symbols displayed inthe operation keys in accordance with the display data stored in thefirst memory 153, and the images such as characters, numerals, andsymbols displayed in the operation keys in accordance with the displaydata stored in the second memory 154 have mutually differing directions.

[0196] Note that, although an example having two memories for storingthe display data is shown in Embodiment 1, the present invention is notlimited to this structure. The portable information terminal of thepresent invention may have two, or more than two, memories for storingthe display data.

[0197] Further, the operation key memories or the operation key drivercircuit group may also be contained within a component such as amicrochip or an LSI within the portable information terminal. Inaddition, a dedicated LSI may also be formed for the operation keymemories or the operation key driver circuit group.

[0198] Further, it is not necessary for the operation keys to alwaysperform display, and a structure in which light is emitted and displayis performed only when required may also be used. For example, when theportable information terminal is utilized as a portable telephone,display may be performed in all of the operation keys only within afixed period when any one of the operation keys is pressed. If theportable information terminal is used as a mobile computer, display maybe always performed in the operation keys even when there is no input tothe operation keys because it is necessary for the operator to always beable to differentiate between the operation keys. Electric powerconsumption can be suppressed in accordance with the above structure.

[0199] Embodiment 2

[0200] A structure of an EL display device used in a display portion ofa portable information terminal of the present invention is explained indetail in Embodiment 2.

[0201] The portable information terminal of Embodiment 2 uses an ELdisplay device in a display portion, and therefore it is not necessaryto use a backlight, differing from a portable information terminal usinga liquid crystal display device. The portable information terminal canconsequently be made smaller, lighter, and thinner. The EL displaydevice is a self light emitting type display device, and therefore has awider angle of view compared with the liquid crystal display device.

[0202]FIG. 6 shows a structure of the pixel portion of the EL displaydevice of Embodiment 2. Reference numeral 600 denotes a display portion,and the display portion has source signal lines S1 to Sx, electric powersource supply lines V1 to Vx, and gate signal lines G1 to Gy. A regioncontaining one of the source signal lines S1 to Sx, one of the electricpower source supply lines V1 to Vx, and one of the gate signal lines G1to Gy is a pixel 602.

[0203] The pixel 602 has a switching TFT 602, an EL driver TFT 603, anEL element 604, and a storage capacitor 605. Note that, although astructure having the storage capacitor 605 is shown in Embodiment 2, thepresent invention is not limited to this structure, and a structure inwhich the storage capacitor 605 is not formed may also be used.

[0204] A gate electrode of the switching TFT 602 is connected to any oneof the gate signal lines G1 to Gy. Further, one of a source region and adrain region of the switching TFT 602 is connected to one of the sourcesignal lines S1 to Sx, while the other is connected to a gate electrodeof the EL driver TFT 603 and to the storage capacitor 605, respectively.

[0205] A source region of the EL driver TFT 603 is connected to any oneof the electric power source supply lines V1 to Vx. Further, a drainregion of the EL driver TFT 603 is connected to one of an anode and acathode of the EL element 604.

[0206] Note that n-channel TFT s and p-channel TFTs may be used for theswitching TFT 602 and for the EL driver TFT 603. However, in a case thedrain region of the EL driver TFT 603 is connected to the anode of theEL element 604, it is preferable that the EL driver TFT 603 be ap-channel TFT. Conversely, in a case the drain region of the EL driverTFT 603 is connected to the cathode of the EL element 604, it ispreferable that the EL driver TFT 603 be an n-channel TFT.

[0207] Embodiment 3

[0208] An example of a driver circuit of the EL display device shown byEmbodiment 2 is explained in Embodiment 3.

[0209]FIG. 7 shows a block diagram of the EL display device ofEmbodiment 3. Reference numeral 620 denotes a source signal line drivercircuit, and reference numeral 622 denotes a gate signal line drivercircuit, and both of the driver circuits control the driving of theswitching TFT 602 and the EL driver TFT 603.

[0210] The source signal line driver circuit 620 has a shift register620 a, a latch (A) 620 b, and a latch (B) 620 c. A clock signal CLK anda start pulse SP are input to the shift register 620 a in the sourcesignal line driver circuit 620. The shift register 620 a generatestiming signals in order based upon the clock signal CLK and the startpulse SP, and supplies the timing signals one after another todownstream circuits.

[0211] Note that the timing signals from the shift register circuit 620a may be buffer amplified by a circuit such as a buffer (not shown inthe figure) and then supplied one after another to the downstreamcircuits as buffer amplified timing signals. The load capacitance(parasitic capacitance) of a wiring which supplies the timing signals islarge because many of the circuits and elements are connected to thewiring. The buffer is formed in order to prevent bluntness in the riseand fall of the timing signal, generated due to the large loadcapacitance.

[0212] The timing signals from the shift register 620 a are supplied tothe latch (A) 620 b. The latch (A) 620 b has a plurality of latch stagesfor processing digital data signals containing image information. Thelatch (A) 620 b writes in and maintains a digital signal simultaneouslywith the input of the timing signal.

[0213] Note that the digital data signal may also be input in order tothe plurality of latch stages of the latch (A) 620 b when writing in thedigital data signal to the latch(A) 620 b. However, the presentinvention is not limited to this structure. The plurality of latchstages of the latch (A) 620 b may be divided into a number of groups,and the digital data signal may be input to the respective groups at thesame time in parallel, performing partitioned driving. Note that, atthis time the number of groups is referred to as partitioned number. Forexample, this is referred to as partitioned drive with 4 divisions whenthe latches are divided into groups every four stages.

[0214] The period until the digital data signal is completely writteninto all of the latch stages of the latch (A) 620 b is referred to as aline period. Namely, the line period begins at the point when thedigital data signal is written into the leftmost stage latch within thelatch (A) 620 b, and is completed when the digital data signal iswritten into the rightmost stage latch. In practice, there are timeswhen the line period includes the addition of a horizontal return periodto the above line period.

[0215] A latch signal is supplied to the latch (B) 620 c when one lineperiod is complete. The digital data signal written into and stored inthe latch (A) 620 b is sent all at once at this instant to the latch (B)620 c, and is written into all of the stage latches of the latch (B) 620c, and stored.

[0216] Write in of the digital data signal is again performed, in order,to the latch (A) 620 b after it has completed sending the digital datasignal to the latch (B) 620 c, based on the timing signal from the shiftregister 620 a.

[0217] The digital data signal written into and stored in the latch (B)620 b is input to source signal lines S1 to Sx during the second oneline period.

[0218] On the other hand, the gate signal line driver circuit 622 has ashift register and a buffer, respectively (both not shown in thefigure). Further, the gate signal line driver circuit 622 may also havea level shifter in addition to the shift register and the buffer,depending upon the circumstances.

[0219] A gate signal from the shift register (not shown in the figure)supplied to the buffer (not shown in the figure), and is supplied to thecorresponding gate signal line in the gate signal line driver circuit622. The gate electrodes of the switching TFTs 602 for one line portionof pixels are connected to the gate signal lines G1 to Gy, and theswitching TFTs 602 of all of the one line portion of pixels must beplaced in an ON state simultaneously. A circuit in which a largeelectric current is capable of flowing is therefore used in the buffer.

[0220] Note that the number, structure, and operation of the sourcesignal line driver circuits and the gate signal line driver circuits isnot limited to the structure shown by Embodiment 3. It is also possibleto use known source signal line driver circuits and known gate signalline driver circuits for the EL display device of Embodiment 3.

[0221] A timing chart for a case of performing 2⁶ gray scale display bythe EL display device of Embodiment 3 and in accordance with a displayperiod separated driving method, one type of time partitioned driving,is shown in FIG. 8. Note that, although an example of performing 2⁶ grayscale display is shown by Embodiment 3, Embodiment 3 is not limited to2⁶ gray scales, and it is possible for the implementor to suitablydetermine the number of digital signal bits.

[0222] Time is shown in the horizontal axis in the timing chart of FIG.8, while the position of the gate signal lines is shown in the verticalaxis.

[0223] One frame period is divided into six subframe periods SF1 to SF6.Note that a period during which one image is displayed in all of thepixels of the display portion is referred to as one frame period F. Anormal EL display device operates with an oscillation frequency equal toor greater than 60 Hz; namely, 60 or more frame periods are formed inone second, and 60 or more images are displayed in one second. If thenumber of images displayed during one second becomes fewer than 60,image flicker or the like begins to become visually conspicuous. Notethat the plurality of periods into which one frame period is divided arereferred to as subframe periods. The number of divisions of one frameperiod increases along with greater numbers of gray scales, and thedriver circuit must be driven at high frequency.

[0224] One subframe period is divided into a write in period Ta and adisplay period Ts. The write in period is a period within one subframeperiod during which a digital signal is input to all of the pixels. Thedisplay period (also referred to as turn on period) is a period duringwhich the EL elements are selected to be in a light emitting state or anon-light emitting state, and display is performed.

[0225] The length of the write in periods Ta1 to Ta6 of the n subframeperiods SF1 to SF6, respectively, are all fixed. The display periods Tsof the subframe periods SF1 to SF6 become display periods Ts1 to Ts6,respectively.

[0226] The length of the display periods is set so as to becomeTs1::Ts2::Ts3:: . . . ::Ts6=2⁰:: 2¹::2²:: . . . ::2⁵. Note that thesubframe periods SF1 to SF6 may be appear in any order. By combining thedisplay periods, a desired gray scale display can be performed fromamong 2⁶ gray scales.

[0227] First, in the write in period, the electric potential (electricpower source electric potential) of the electric power source supplylines V1 to Vx is maintained at the same height as the electricpotential of an opposing electrode (opposing electric potential). Theheight of the electric power source electric potential may be set to thesame height as the opposing electric potential within a range in whichthe EL elements do not emit light. Note that the electric power sourceelectric potential is always maintained at a fixed level. Further, theelectric potential difference between the opposing electric potentialand the electric power source electric potential is referred to as an ELdriver voltage. It is preferable that the EL driver voltage be 0 Vduring the write in period, but it may have any size such that the ELelements do not emit light.

[0228] All of the switching TFTs 602 connected to the gate signal lineG1 are placed into an ON state by the gate signal input to the gatesignal line G1. A digital data signal is input into the source signallines (S1 to Sx) at the same time. The digital data signal contains “0”and “1” information, and one of the digital data signals “0” and “1” hasHI electric voltage, while the other has LO voltage.

[0229] The digital signal input into the source signal lines (S1 to Sx)is then input to the gate electrodes of the EL driver TFTs 603 throughthe switching TFTs 602, which are in the ON state.

[0230] Next, by the gate signal input to the gate signal line G2. all ofthe switching TFTs 602 connected to the gate signal line G2 are placedin the ON state. The digital signal is then input to the source signallines (S1 to Sx).

[0231] The digital data signal input to the source signal lines (S1 toSx) is input to the gate electrodes of the EL driver TFTs 603 throughthe switching TFTs 602 in the ON state.

[0232] By repeating the above operations for the gate signal lines G3 toGy, the digital data signal is input to the gate electrodes of the ELdriver TFFs of all of the pixels. The period up until the digital datasignal is input to the gate electrode of the EL driver TFT 603 of all ofthe pixels is the write in period.

[0233] The display period commences at same time as when the write inperiod is complete. All of the switching TFTs 602 are set into the OFFstate in the display period. The electric power source electricpotential is then set so as to have an electric potential differencewith the opposing electric potential on an order such that the ELelements 604 emit light.

[0234] When the digital signal input to the gate electrode of the ELdriver TFTs 603 has “0” information, the EL driver TFTs 603 are set intothe OFF state in Embodiment 3. The pixel electrodes of the EL elements604 are therefore maintained at an electric potential which has the sameheight as the opposing electric potential. As a result, the EL elements604 having pixels to which the digital signal containing “0” informationis applied do not emit light.

[0235] Conversely, in this embodiment, the EL driver TFTs 603 are placedinto the ON state in a case the digital signal has “1” information. Theelectric potential of the pixel electrodes of the EL elements 604 aretherefore maintained at the electric power source electric potential.Further, the opposing electric potential has an electric potentialdifference with the electric power source electric potential on an ordersuch that the EL elements 604 emit light. As a result, the EL elements604 having pixels to which the digital signal containing “1” informationis applied emit light.

[0236] Note that, although the EL driver TFTs 603 are in the OFF statein a case the digital signal has “0” information, and although the ELdriver TFTs 603 are in the ON state when the digital signal has “1”information in Embodiment 3, the present invention is not limited tothis structure. A structure in which the EL driver TFTs 603 are placedin the ON state when the digital signal has “0” information, and inwhich the EL driver TFTs 603 are placed in the OFF state when thedigital signal has “1” information may also be used.

[0237] Whether the EL elements are placed in a state of emitting lightor not emitting light is thus selected in accordance with theinformation in the digital signal, and display is performed in all ofthe pixels at once. An image is formed by performing display in all ofthe pixels. The period during which the pixels perform display isreferred to as the display period.

[0238] The display period is any of the display periods Ts1 to Ts6.Predetermined pixels are turned on in the display period Ts1 here.

[0239] Next, the write in period is entered again, and the displayperiod begins once the digital signal is input to all of the pixels. Atthis point the display period becomes any of the display periods Ts2 toTs6. Predetermined pixels are turned on in the display period Ts2 here.

[0240] Similar operations are subsequently repeated in the fourremaining subframe periods, and predetermined pixels are turned on inthe display periods within the respective subframe periods.

[0241] One frame period ends when the six subframe periods appear. Thegray scale of each pixel is determined by adding the lengths of thedisplay periods in which each pixels is turned on.

[0242] Note that the EL display device controls the emission of lightfrom the EL elements in Embodiment 3 by always maintaining the opposingelectric potential at a fixed electric potential, changing the write inperiods and the display periods, and changing the size of the EL drivervoltage. However, the present invention is not limited to thisstructure. The EL display device of the present invention may alsocontrol the light emission of the EL elements by always maintaining afixed electric power source electric potential and changing the opposingelectric potential.

[0243] The source signal line driver circuit 620 and the gate signalline driver circuit 622 may also be mounted on the substrate on whichthe display portion 600 is formed in Embodiment 3 by using a componentsuch as an IC chip. In this case, the structure becomes one in which thesource signal line driver circuit 620 and the gate signal line drivercircuit 622 on the IC chip are connected to the display portion 600through a connector such as an FPC or TAB. The EL display devicecontains the source signal line driver circuit 620 and the gate signalline driver circuit 622 on the IC chip in this case.

[0244] Note that it is possible to implement Embodiment 3 by freelycombining it with Embodiment 1 or Embodiment 2.

[0245] Embodiment 4

[0246] An example of a driver circuit of the EL display device shown byEmbodiment 2 is explained in Embodiment 4.

[0247]FIG. 9 shows a top surface view of an EL display device ofEmbodiment 4. Reference numeral 630 denotes a source signal line drivercircuit, reference numeral 632 denotes a gate signal line drivercircuit, and reference numeral 600 denotes the display portion. One eachof the source signal line driver circuit and the gate signal line drivercircuit are formed in Embodiment 4, but the present invention is notlimited to this structure. Two source signal line driver circuits may beformed, and two gate signal line driver circuits may also be formed.

[0248] The source signal line driver circuit 630 has a shift register630 a, a level shift 630 b, and a sampling circuit 630 c. Note that thelevel shift 630 b may be used when necessary, and need not always beused. Further, the structure in Embodiment 4 has the level shift 630 bformed between the shift register 630 a and the sampling circuit 630 c,but Embodiment 4 is not limited to this structure. A structure in whichthe level shift 630 b is incorporated within the shift register 630 amay also be used.

[0249] Electric power source supply lines V1 to Vx are maintained at afixed electric potential (electric power supply electric potential) bybeing connected to an electric power source.

[0250] Further, the gate signal line driver circuit 632 has a shiftregister and a buffer (both not shown in the figure). The gate signalline driver circuit 632 may also have a level shift.

[0251] A clock signal CLK, which is a panel control signal, and a startpulse signal SP are input to the shift register 630 a. A sampling signalfor sampling an analog signal having image information is output fromthe shift register 630 a. The output sampling signal is input to thelevel shift 630 b, the amplitude of its electric potential is madelarger, and then the sampling signal is output.

[0252] The sampling signal output from the level shift 630 b is input tothe sampling circuit 630 c. The analog signal is simultaneously input tothe sampling circuit 630 c through an analog signal line.

[0253] The input analog signal is sampled in accordance with thesampling signal in the sampling circuit 630 c, and is input to eachsource signal lines S1 to Sx.

[0254] A timing chart for a case of driving the EL display device ofEmbodiment 4 by an analog method is shown in FIG. 10. A period from theselection of one gate signal line until the selection of the next,different gate signal line is referred to as one line period L. Notethat in this specification the selection of the gate signal line denotesa gate signal, having an electric potential such that a switching TFTbecomes placed in the ON state, being input to a gate signal line.

[0255] Further, a period from when one image is displayed until the nextimage is displayed corresponds to one frame period F. There are y gatesignal lines in the case of the EL display device of Embodiment 4, andtherefore y line periods L1 to Ly are formed within one frame period.

[0256] First, the electric power source electric potential of theelectric power source supply lines V1 to Vx is always maintained at afixed value in Embodiment 4. The electric potential of opposingelectrodes is also maintained at a fixed value. The electric potentialof the opposing electrodes has an electric potential difference with theelectric power source electric potential of an order at which the ELelements emit light when the electric power source electric potential isimparted to pixel electrodes of the EL elements 604.

[0257] The gate signal line G1 is selected in the first line period L1in accordance with the gate signal input from the gate signal linedriver circuit 632 through the gate signal line G1, and all of theswitching TFTs connected to the gate signal line G1 are placed in the ONstate. The analog signal is then input from the source signal linedriver circuit 630 to the source signal lines S1 to Sx in order. Theanalog signal input to the source signal lines S1 to Sx is input to thegate electrodes of the EL driver TFTs 603 through the switching TFTs602.

[0258] The amount of electric current flowing in channel forming regionsof the EL driver TFTs 603 is controlled in accordance with a gatevoltage Vgs, which is the electric potential difference between gateelectrodes and source regions of the EL driver TFTs 603. The electricpotential imparted to the pixel electrodes of the EL elements 604 istherefore determined by the electric potential of the analog signalinput to the gate electrodes of the EL driver TFTs 603. The EL elements604 are therefore controlled by the electric potential of the analogsignal and performs light emission.

[0259] When the above operations are repeated and input of the analogsignal to the source signal lines S1 to Sx is completed, the first lineperiod L1 is complete. Note that a period until the completion of theanalog signal input to the source signal lines S1 to Sx may also becombined with a horizontal return period and taken as one line period.The second line period L2 begins next, the gate signal line G2 isselected by the gate signal, and the analog signal is input in order tothe source signal lines S1 to Sx, similar to the first line period L1.

[0260] All of the line periods L1 to Ly are complete when all of thegate signal lines G1 to Gy are selected. One frame period is thencomplete when all of the line periods L1 to Ly are completed. One imageis formed within one frame period by performing display in all of thepixels. Note that all of the line periods L1 to Ly and a horizontalreturn period may also be combined and taken as one frame period.

[0261] The amount of light emitted by the EL elements is thus controlledin accordance with the electric potential of the analog signal, and grayscale display is performed in accordance with the control of the amountof light emitted.

[0262] The source signal line driver circuit 630 and the gate signalline driver circuit 632 may also be mounted on the substrate on whichthe display portion 600 is formed in Embodiment 4 by using a componentsuch as an IC chip. In this case, the structure becomes one in which thesource signal line driver circuit 630 and the gate signal line drivercircuit 632 on the IC chip are connected to the display portion 600through a connector such as an FPC or TAB. The EL display devicecontains the source signal line driver circuit 630 and the gate signalline driver circuit 632 on the IC chip in this case.

[0263] Note that it is possible to implement Embodiment 4 by freelycombining it with Embodiment 1 or Embodiment 2.

[0264] Embodiment 5

[0265] An EL display device having a structure which differs from thatof Embodiments 2 to 4 is explained in Embodiment 5.

[0266] An example of a block diagram of an EL display device of thepresent invention is shown in FIG. 11. The EL display device of FIG. 11has a display portion 700 formed on a substrate by TFTs, a source signalline driver circuit 702 arranged in the periphery of the display portion700, a write in gate signal line driver circuit (a first gate signalline driver circuit)703, and an erasure gate signal line driver circuit(a second gate signal line driver circuit) 704. Note that, although theEL display device has one source signal line side driver circuit inEmbodiment 5, two source signal line side driver circuits may also beused.

[0267] The source signal line driver circuit 702 has at least a shiftregister 702 a, a latch (A) 702 b, and a latch (B) 702 c.

[0268] A clock signal CLK and a start pulse SP are input to the shiftregister 702 a in the source signal line driver circuit 702. The shiftregister 702 a generates timing signals in order based upon the clocksignal CLK and the start pulse SP, and supplies the timing signals oneafter another to downstream circuits through a circuit such as a buffer(not shown in the figure).

[0269] The timing signals from the shift register circuit 702 a may alsobe buffer amplified by such as the buffer (not shown in the figure). Theload capacitance (parasitic capacitance) of a wiring which supplies thetiming signals is large because many of the circuits and elements areconnected to the wiring. The buffer is formed in order to preventbluntness in the rise and fall of the timing signal, generated due tothe large load capacitance.

[0270] The timing signals from the shift register 702 a are supplied tothe latch (A) 702 b. The latch (A) 702 b has a plurality of latch stagesfor processing n-bit digital data signals containing image information.The latch (A) 702 b writes in and maintains an n-bit digital signalsupplied from external of the EL display device and simultaneously withthe input of the timing signal.

[0271] Note that the digital signal may also be input in order to theplurality of latch stages of the latch (A) 702 b when writing in then-bit digital signal to the latch(A) 702 b. However, the presentinvention is not limited to this structure. The plurality of latchstages of the latch (A) 702 b may be divided into a number of groups,and the digital signal may be input to the respective groups at the sametime in parallel, performing namely partitioned driving. Note that, thenumber of groups is called the partitioned number. For example, this isreferred to as gray scale drive with 4 divisions when the latches aredivided into groups every four stages.

[0272] The period until the digital signal is completely written intoall of the latch stages of the latch (A) 702 b is referred to as a lineperiod. Namely, the line period begins at the point when the digitalsignal is written into the leftmost stage latch within the latch (A) 702b, and is completed when the digital signal is written into therightmost stage latch. In practice, there are times when the line periodincludes the addition of a horizontal return period to the above lineperiod.

[0273] A latch signal is supplied to the latch (B) 702 c when one lineperiod is finished. The digital signal written into and stored in thelatch (A) 702 b is sent all at once at this instant to the latch (B) 702c, and is written into all of the stage latches of the latch (B) 702 c,and stored.

[0274] Write in of the digital signal supplied external from the ELdisplay device is again performed, in order, to the latch (A) 702 bafter it has completed sending the digital signal to the latch (B) 702c, based on the timing signal from the shift register 702 a.

[0275] The digital signal written into and stored in the latch (B) 702 bis input to source signal lines S1 to Sx during the second one lineperiod.

[0276] On the other hand, the write in gate signal line driver circuit703 and the erasure gate signal line driver circuit 704 each have ashift register and a buffer (both not shown in the figure). Further, thewrite in gate signal line driver circuit 703 and the erasure gate signalline driver circuit 704 may also have a level shifter in addition to theshift register and the buffer, depending upon the circumstances.

[0277] A timing signal is supplied from the shift registers (not shownin the figure) to the buffers (not shown in the figure) in the write-ingate signal line driver circuit 703 and the erasure gate signal linedriver circuit 704, and then is supplied to the corresponding gatesignal lines (also referred to as scanning lines). The gate electrodesof one line portion of pixel TFTs are connected to the gate signal line,and the one line portion of pixel TFTs must all be placed in an ON statesimultaneously. A circuit in which a large electric current is capableof flowing is therefore used in the buffer.

[0278] The source signal line driver circuit 702, the write in gatesignal line driver circuit 703, and the erasure gate signal line drivercircuit 704 may also be formed in the substrate on which the displayportion 700 is formed in Embodiment 5 or by using a component such as anIC chip to mount on a substrate with a display portion 700. In thiscase, the structure becomes one in which the source signal line drivercircuit 702, the write in gate signal line driver circuit 703, and theerasure gate signal line driver circuit 704 on the IC chip are connectedto the display portion 700 through a connector such as an FPC or TAB.The EL display device contains the source signal line driver circuit702, the write in gate signal line driver circuit 703, and the erasuregate signal line driver circuit 704 on the IC chip in this case.

[0279]FIG. 12 shows a blow up of the display portion 700. The sourcesignal lines S1 to Sx connected to the latch (B) 702 c of the sourcesignal line driver circuit 702; electric power source supply lines V1 toVx connected to an electric power source external to the EL displaydevice; write in gate signal lines (first gate signal lines) Ga1 to Gayconnected to the write in gate signal line driver circuit 703; anderasure gate signal lines (second gate signal lines) Ge1 to Geyconnected to the erasure gate signal line driver circuit 704 are formedin the display portion 700.

[0280] A region containing one each of: the source signal lines S1 toSx; the electric power source supply lines V1 to Vx; the write in gatesignal lines Ga1 to Gay; and the erasure gate signal lines Ge1 to Gey isa pixel 705. A plurality of the pixels 705 are arranged in a matrixshape in the display portion 700.

[0281] Reference numeral 707 within the pixel 705 denotes a switchingTFT. A gate electrode of the switching TFT 707 is connected to one ofthe write in gate signal lines Ga1 to Gay. One of a source region and adrain region of the switching TFT 707 is connected to one of the sourcesignal lines S1 to Sx, and the other is connected to a gate electrode ofan EL driver TFT 708 and to a storage capacitor 712. Further, thestorage capacitor 712 is connected to one of the electric power sourcesupply lines V1 to Vx.

[0282] The storage capacitor 712 is formed in order to maintain the gatevoltage of the EL driver TFF 708 when the switching TFT 707 is in anon-selected state (OFF state). Note that, although a structure in whichthe storage capacitor 712 is formed is shown in Embodiment 5, thepresent invention is not limited to this structure, and a structure inwhich the storage capacitor 712 is not formed may also be used.

[0283] Further, a source region of the EL driver TFT 708 is connected toone of the electric power source supply lines V1 to Vx, and a drainregion is connected to an anode or a cathode of an EL element 710.

[0284] One of a source region and a drain region of the erasure TFT 709is connected to a gate electrode of the EL driver TFT 708, and the otheris connected to one of the electric power source supply lines V1 to Vx.A gate electrode of the erasure TFT 709 is connected to one of theerasure gate signal lines Ge1 to Gey.

[0285] The EL element 710 is composed of an anode, a cathode, and an ELlayer formed between the anode and the cathode. When the anode isconnected to the drain region of the EL driver TFT 708, the anodebecomes a pixel electrode and the cathode becomes an opposing electrode.Conversely, if the cathode is connected to the drain region of the ELdriver TFT 708, then the cathode becomes the pixel electrode and theanode becomes the opposing electrode.

[0286] An opposing electric potential is imparted to the opposingelectrode of the EL element 710. The electric potential differencebetween the opposing electric potential and the electric power sourceelectric potential is always maintained in Embodiment 5 at an electricpotential difference on an order at which the EL element emits lightwhen the electric power source electric potential is imparted to thepixel electrode. The electric power source electric potential and theopposing electric potential are imparted to the EL display device of thepresent invention in accordance with an electric power source formed ina component such as an external IC.

[0287] In typical EL display devices at present, the necessary amount ofelectric current per surface area of the display portion is on the orderof several mA/cm² when the amount of light emitted per surface area ofthe pixel has a luminescence of 200 cd/m². In particular, therefore, ifthe size of the screen area becomes large, the height of the electricpotential imparted from the electric power source formed in the ICbecomes difficult to control by a switch. The electric power sourceelectric potential and the opposing electric potential are alwaysmaintained as fixed in Embodiment 5, and the height of the electricpotential imparted from the electric power source formed in the IC neednot be controlled by a switch. Embodiment 5 is therefore useful inachieving a panel having a larger screen size.

[0288] The switching TFT 707, the EL driver TFT 708, and the erasure TFT709 can either use n-channel TFTs or p-channel TFTs. Further, theswitching TFT 707, the EL driver TFT 708, and the erasure TFT 709 mayhave, in addition to a single gate structure, a multi-gate structuresuch as a double gate structure of a triple gate structure.

[0289] Note that it is preferable that the EL driver TFT 708 be ap-channel TFT for cases in which the drain region of the EL driver TFT708 is connected to the anode of the EL element 710. On the other hand,it is preferable that the EL driver TFT 708 be an n-channel TFT forcases in which the drain region of the EL driver TFT 708 is connected tothe cathode of the EL element 710.

[0290] Next, a timing chart for a case of performing 2⁶ gray scaledisplay with the EL display device of Embodiment 5 in accordance withsimultaneous erasing scan driving, one method of time partitioned drive,is shown in FIG. 13. Note that, although an example of performing 2⁶gray scale display is explained by Embodiment 5, the present embodimentis not limited to 2⁶ gray scales, and it is possible for an operator tosuitably determine the number of digital signal bits.

[0291] The horizontal axis shows time and the vertical axis shows gatesignal lines in the timing chart of FIG. 13.

[0292] First, the switching TFTs 707 of all pixels connected to thewrite in gate signal line Ga1 (a first line of pixels) are placed in theON state in accordance with a write in gate signal input to the write ingate signal line Ga1 from the write in gate signal line driver circuit703.

[0293] The first bit of the digital signal is then input simultaneouslyto the source signal lines S1 to Sx from the latch (B) 702 c of thesource signal line driver circuit 702. The digital signal is input tothe gate electrodes of the EL driver TFTs 708 through the switching TFTs707. The digital signal has “0” or “1” information, and one of the “0”and “1” digital signals is a signal having HI voltage, while the otheris a signal having LO voltage.

[0294] In a case the digital signal has “0” information, the EL driverTFTs 708 are placed in the OFF state in Embodiment 5. The electric powersource electric potential is therefore not imparted to the pixelelectrode of the EL elements 710. As a result, the EL elements 710 ofpixels into which the digital signals having “0” information are inputdo not emit light.

[0295] Conversely, the EL driver TFTs 708 are placed in the ON statewhen a digital signal having “1” information is input. The electricpower source electric potential is therefore imparted to the pixelelectrodes of the EL elements 710. As a result, the EL elements 710 ofpixels into which the digital signals having “1” information are inputemit light.

[0296] Note that, although the EL driver TFTs 708 are in the OFF statewhen the digital signal has “0” information, and although the EL driverTFTs 708 are in the ON state when the digital signal has “1” informationin Embodiment 5, the present invention is not limited to this structure.A structure in which the EL driver TFTs 708 are placed in the ON statewhen the digital signal has “0” information, and in which the EL driverTFTs 708 are placed in the OFF state when the digital signal has 1information may also be used.

[0297] The EL elements 710 are placed in a state of emitting light ornot emitting light at the same time that the digital signal is input tothe first line of pixels, and the first line of pixels perform display.A period during which the pixels perform display is referred to as adisplay period Tr. In particular, the display period which begins byinput of the first bit of the digital signal to the pixels is referredto as a display period Tr1. The timing at which the display periods ofeach line begin have time differences.

[0298] Next, the switching TFTs 707 of all pixels connected to the writein gate signal line Ga2 are placed in the ON state in accordance withthe write in gate signal input to the write in gates signal line Ga2 atthe same time as the selection of the next gate signal line Ga1 iscompleted. The first bit of the digital signal is then input to thesecond line pixels from the source signal lines S1 to Sx.

[0299] Note that the input of the signal to the pixels denotes the inputof the signal to the gate electrode of the EL driver TFT through theswitching TFF of the pixel in Embodiment 5.

[0300] All of the write in gate signal lines Ga1 to Gax are thenselected in order in accordance with the write in gate signal input toall of the write in gate signal lines Ga1 to Gax. The first bit of thedigital signal is then input to all of the lines of pixels. A perioduntil the first bit of the digital signal is input to the pixels of alllines denotes a write in period Ta1.

[0301] On the other hand, before the first bit of the digital signal isinput to all of the lines of pixels, namely before the write in periodTa1 is complete, the erasure gate signal line Ge1 is selected inaccordance with an erasure gate signal input from the erasure gatesignal line driver circuit 704 in parallel with the input of the firstbit of the digital signal to the pixels.

[0302] The erasure TFTs 709 of all the pixels (the first line of pixels)connected to the erasure gate line Ge1 are then placed in an ON state inaccordance with the erasure gate signal input to the erasure gate signalline Ge1. The electric power source electric potentials of the electricpower source supply lines V1 to Vx are then imparted to the gateelectrodes of the EL driver TFTs 708 through the erasure TFT 709.

[0303] The gate electrode and the source region of the EL driver TFT 708are maintained at the same electric potential height when the electricpower source electric potential is imparted to the gate electrode of theEL driver TFT 708, and therefore the EL driver TFTs 708 are place in theOFF state. The electric power source electric potential consequently isnot imparted to the pixel electrodes of the EL elements 710, and all ofthe EL elements of the first line of pixels then become placed in thenon-light emitting state so that the first line of pixels do not performdisplay. In other words, the digital signals stored by the gateelectrodes of the EL driver TFTs 708 from the point at which the writein gate signal line Ga1 is selected in accordance with the write in gatesignal are thus erased by imparting the electric power source electricpotential to the gate electrodes of the EL driver TFTs 708. The firstline of pixels therefore do not perform display.

[0304] A period during which the pixels do not perform display isreferred to as a non-display period Td. For the first line of pixels,the display period Tr1 is completed at the same time as the erasure gatesignal is input to the erasure gate signal line Ge1, and the non-displayperiod Td1 thus begins. Then, similar to the display period Tr, thetiming at which the non-display period Td begins in each line has a timedifferences for each line.

[0305] The erasure TFTs 709 of all the pixels (the second line ofpixels) connected to the erasure gate signal line Ge2 are then placed inan ON state in accordance with the erasure gate signal input to theerasure gate signal line Ge2 at the same time as when the selection ofGe1 is complete. The electric power source electric potentials of theelectric power source supply lines V1 to Vx are then imparted to thegate electrodes of the EL driver TFTs 708 through the erasure TFT 709.The EL driver TFTs 708 are placed in the OFF state when the electricpower source electric potential is imparted to the gate electrodes ofthe EL driver TFTs 708. The electric power source electric potential istherefore not imparted to the pixel electrodes of the EL elements 710.As a result, the EL elements of the second line of pixels are all placedin a non-light emitting state, and display is no longer performed in thesecond line of pixels, becoming a non-display state.

[0306] The erasure gate signal is the input to all of the erasure gatesignal lines in order. A period until all of the erasure gate signallines (Ga1 to Gax) are selected and the first bit of the digital signalstored in all the lines of pixels is erased is referred to as an erasureperiod Te1.

[0307] On the other hand, before the first bit of the digital signalstored in all the lines of pixels is erased, namely before the erasureperiod Te1 is complete, the write in gate signal line Ga1 is selected inaccordance with the write in gate signal input from the write in gatesignal line driver circuit 704. This occurs in parallel with the erasureof the first bit of the digital signal in the pixels. Display again isperformed in the first line of pixels as a result, the non-displayperiod Td1 finished, and a display period Tr2 begins.

[0308] All of the write in gate signal lines are similarly selected inorder, and the second bit of the digital signal is input to all of thepixels. A period until the input of the second bit of the digital signalis finished to all the lines of pixels is referred to as the write inperiod Ta2.

[0309] On the other hand, before the second bit of the digital signalinput to all the lines of pixels is erased, namely before the write inperiod Ta2 is complete, the erasure gate signal line Ge2 is selected inaccordance with the erasure gate signal input from the erasure gatesignal line driver circuit 704. This occurs in parallel with the writein of the second bit of the digital signal in the pixels. The ELelements of the first line of pixels are thus all placed in a non-lightemitting state, and the first line of pixels no longer performs display.The display period Tr2 therefore finishes in the first line of pixels,and a non-display period Td2 begins.

[0310] The erasure gate signal is then input in order to all of theerasure gate signal lines. A period until all of the erasure gate signallines Ga1 to Gax are selected and the second bit of the digital signalstored in all the lines of pixels is erased is an erasure period Te2.

[0311] The above operations are repeatedly performed until the fourthbit of the digital signal is input to the pixels, and the displayperiods Tr and the non-display periods Td repeatedly appear. The displayperiod Tr1 is the period from when the write in period Ta1 begins untilthe erasure period Te1 begins. Further, the non-display period Td1 isthe period from when the erasure period Te1 begins until the displayperiod Tr2 begins. Display periods Tr2 and Tr3, and non-display periodsTd2 and Td3 each then have their periods determined by the write inperiods Ta1, Ta2, Ta3, and Ta4, and the erasure periods Te1, Te2, andTe3, respectively, similar to the display period Tr1 and the non-displayperiod Td1.

[0312] After an m-th-bit of the digital signal is input to the firstline of pixels, the erasure gate signal lines Ge1 to Gey becomeunselected in accordance with the erasure gate signal. For simplicity ofexplanation, an example of a case in which the erasure gate signal linesGe1 to Gey are unselected when the fourth bit of the digital signal isinput is explained in Embodiment 5, but the present invention is notlimited to this. Whether the erasure gate signal lines Ge1 to Gey areselected or unselected when a certain bit of the digital signal is inputcan be arbitrarily selected with the present invention.

[0313] A display period Tr4 begins and the first line of pixels performdisplay when the fourth bit of the digital signal is input to the firstline of pixels. The fourth bit of the digital signal is then stored inthe pixels until the next bit of the digital signal is input.

[0314] The fourth bit of the digital signal stored in the pixels isreplaced by the fifth bit of the digital signal when the fifth bit ofthe digital signal is then input to the first line of pixels. A displayperiod Tr5 thus begins in the first line of pixels, and display isperformed. The fifth bit of the digital signal is stored by the pixelsuntil the next bit of the digital signal is input.

[0315] The fifth bit of the digital signal stored in the pixels isreplaced by the sixth bit of the digital signal when the sixth bit ofthe digital signal is then input to the first line of pixels. A displayperiod Tr6 thus begins in the first line of pixels, and display isperformed. The sixth bit of the digital signal is stored by the pixelsuntil the first bit of the digital signal of the next frame period isinput.

[0316] The display period Tr4 is the period from when the write inperiod Ta4 begins until the write in period Ta5 begins. The displayperiods Tr5 and Tr6 also have their periods determined similar to thatof the display period Tr4, in accordance with the write in periods Ta5,Ta6, and the first write in period Ta1 in the next frame period.

[0317] Note that it is necessary for the sum of the lengths of all ofthe write in periods to be shorter than one frame period in Embodiment5, and in addition, that the length of the display periods be set sothat Tr1::Tr2::Tr3:: . . . ::Tr6=2⁰::2¹::2²:: . . . ::2⁵. Further, it isvery important that the write in periods do not overlap with each other.

[0318] One image can be displayed when the display periods Tr1 to Tr6are complete in all of the pixels. The period during which one image isdisplayed is referred to as one frame period F in the driving method ofthe present invention.

[0319] After one frame period is complete, a write in gate signal isonce again input to the write in gate signal line Ga1 from the write ingate signal line driver circuit 703. The first bit of the digital signalis input to the pixels as a result, and the display period Tr1 onceagain begins in the first line of pixels. The above stated operationsare then repeated again.

[0320] It is preferable to form 60 or more frame periods every secondwith a normal EL display device. If the number of images displayed inone second becomes fewer than 60, image flicker starts to becomevisually conspicuous.

[0321] The gray scale displayed by a pixel during one frame period canbe set by finding the total sum of the lengths of the display periodsduring which the EL element of the pixel emits light during the oneframe period.

[0322] It is vital that the write in period Ta4, in which the fourth bitof the digital signal is written in to the pixels, be shorter than thelength of the display period Tr4.

[0323] Further, the display periods Tr1 to Tr6 may appear in any order.For example, it is possible for the display periods to appear such thatTr3, Tr5, Tr2, . . . , follow after Tr1 within one frame period.However, it is preferable that the erasure periods Te1 to Te6 have anorder such that they do not overlap with each other.

[0324] Non-light emitting periods during which display is not performedcan be formed with Embodiment 5. If a completely white image isdisplayed in an EL display device when using a conventional analogdriving method, then the EL elements always emit light and this becomesa cause of quickening EL layer degradation. Non-light emitting periodscan be formed with the present invention, and therefore degradation ofthe EL layers can be suppressed to a certain extent.

[0325] Note that portions of the display periods Tr and the write inperiods Ta overlap in Embodiment 5. In other words, it is possible tohave pixel display even during the write in periods Ta. The ratio of thetotal sum of the lengths of the display periods Tr in one frame period(duty ratio) is therefore determined only by the lengths of the write inperiods Ta.

[0326] Note that it is possible to implement Embodiment 5 by freelycombining it with Embodiment 1.

[0327] Embodiment 6

[0328] In Embodiment 6, a method of manufacturing a display portionhaving an EL display device, and TFTs (n-channel TFTs and p-channelTFTs) of a driver circuit formed in the periphery of the displayportion, on the same substrate simultaneously is explained in detail.

[0329] First, as shown in FIG. 14A, a base film 401 made from aninsulating film such as a silicon oxide film, a silicon nitride film, ora silicon nitride oxide film is formed on a substrate 400 made fromglass such as barium borosilicate glass or aluminum borosilicate glass,typically Corning Corp. #7059 glass or #1737 glass, or made from aquartz substrate. For example, a silicon nitride oxide film made fromSiH₄, NH₃, and N₂O by plasma CVD is formed with a thickness of 10 to 200nm (preferably from 50 to 100 nm), and a hydrogenized silicon nitrideoxide film with a thickness of 50 to 200 nm (preferably between 100 and150 nm), made from SiH₄ and N₂O, is similarly formed and laminated. Notethat the base film is shown as one layer in FIG. 14A. The base film 401is shown as a two layer structure in Embodiment 6, but it may also beformed as a single layer of the above insulating films, and it may alsobe formed having a lamination structure in which two layers or more arelaminated.

[0330] Semiconductor layers 402 to 405 are formed by a crystallinesemiconductor film manufactured using a laser crystallization method ofa semiconductor film having an amorphous structure, or using a knownthermal crystallization method. The thickness of the semiconductorlayers 402 to 405 is formed to a thickness of 25 to 80 nm (preferablybetween 30 and 60 nm). There are no limitations in the crystallinesemiconductor film material, but it is preferable to form the film froma semiconductor material such as silicon or a silicon germanium (SiGe)alloy.

[0331] As for known crystallization methods, there is a thermalcrystallization method using an electric furnace, a laser annealingcrystallization method using laser light, a lamp annealingcrystallization method using infrared light, and a crystallizationmethod using a catalyst metal.

[0332] A laser such as a pulse emission type or continuous emission typeexcimer laser, a YAG laser, and a YVO₄ laser can be used in the lasercrystallization method to manufacture a crystalline semiconductor film.A method of condensing laser light emitted from a laser emission deviceinto a linear shape by an optical system and then irradiating the lightto the semiconductor film may be used when these types of lasers areused. The crystallization conditions may be suitably selected by theoperator, but when using the excimer laser, the pulse emission frequencyis set to 300 Hz, and the laser energy density is set from 100 to 400mJ/cm² (typically between 200 and 300 mJ/cm²). Further, the secondharmonic is utilized when using the YAG laser, the pulse emissionfrequency is set from 30 to 300 KHz, and the laser energy density may beset from 300 to 600 mJ/cm² (typically between 350 and 500 mJ/cm²). Thelaser light collected into a linear shape with a width of 100 to 1000μm, for example 400 μm, is then irradiated over the entire surface ofthe substrate. This is performed with an overlap ratio of 50 to 98% forthe linear shape laser light.

[0333] A gate insulating film 406 is formed covering the semiconductorlayers 402 to 405. A gate insulating film 406 is formed by an insulatingfilm containing silicon with a thickness of 40 to 150 nm by plasma CVDor sputtering. A 120 nm thick silicon nitride oxide film is formed inEmbodiment 6. The gate insulating film 406 is not limited to this typeof silicon nitride oxide film, of course, and other insulating filmscontaining silicon may also be used, in a single layer or in alamination structure. For example, when using a silicon oxide film, itcan be formed by plasma CVD with a mixture of TEOS (tetraethylorthosilicate) and O₂, at a reaction pressure of 40 Pa, with thesubstrate temperature set from 300 to 400° C., and by discharging at ahigh frequency (13.56 MHz) electric power density of 0.5 to 0.8 W/cm².Good characteristics as a gate insulating film can be obtained bysubsequently performing thermal annealing, at between 400 and 500° C.,of the silicon oxide film thus manufactured.

[0334] A first conducting film 407 and a second conducting film 408 arethen formed on the gate insulating film 406 in order to form gateelectrodes. The first conducting film 407 is formed from Ta (tantalum)with a thickness of 50 to 100 nm, and the second conducting film 408 isformed from W (tungsten) having a thickness of 100 to 300 nm, inEmbodiment 6.

[0335] The Ta film is formed by sputtering, and sputtering of a Tatarget is performed by Ar. If appropriate amounts of Xe and Kr are addedto Ar at the time of sputtering, the internal stress of the Ta film isrelaxed, and film peeling can be prevented. The resistivity of an αphase Ta film is on the order of 20 μΩcm, and it can be used in the gateelectrode, but the resistivity of a β phase Ta film is on the order of180 μΩcm and it is unsuitable for the gate electrode. An α phase Ta filmcan easily be obtained if a tantalum nitride film, which possesses acrystal structure near that of α phase Ta, is formed with a thickness of10 to 50 nm as a base for Ta in order to form α phase Ta.

[0336] The W film is formed by sputtering with a W target, which canalso be formed by thermal CVD using tungsten hexafluoride (WF₆).Whichever is used, it is necessary to be able to make the film becomelow resistance in order to use it as the gate electrode, and it ispreferable that the resistivity of the W film be made equal to or lessthan 20 μΩcm. The resistivity can be lowered by enlarging the crystalgrains of the W film, but for cases in which there are many impurityelements such as oxygen in the W film, crystallization is inhibited, andthe film becomes high resistance. A W target having a purity of 99.9999%or 99.99% is thus used in sputtering. In addition, by forming the W filmwhile taking sufficient care that no impurities from within the gasphase are introduced at the time of film formation, a resistivity of 9to 20 μΩcm can be achieved.

[0337] Note that, although the first conducting film 407 is Ta and thesecond conducting film 408 is W in Embodiment 6, the conducting filmsare not limited to these, and both may also be formed from an elementselected from the group consisting of Ta, W, Ti, Mo, Al, and Cu, or froman alloy material having one of these elements as its main constituent,or from a chemical compound of these elements. Further, a semiconductorfilm, typically a polysilicon film into which an impurity element suchas phosphorous is doped, may also be used. Examples of preferablecombinations other than that used in Embodiment 6 include: forming thefirst conducting film by tantalum nitride (TaN) and combining it withthe second conducting film formed from W; forming the first conductingfilm by tantalum nitride (TaN) and combining it with the secondconducting film formed from Al; and forming the first conducting film bytantalum nitride (TaN) and combining it with the second conducting filmformed from Cu. (See FIG. 14B.)

[0338] Masks 409 to 412 are formed next from resist, and a first etchingprocess is performed in order to form electrodes and wirings. An ICP(inductively coupled plasma) etching method is used in Embodiment 6. Agas mixture of CF₄ and C1 ₂ is used as an etching gas, and a plasma isgenerated by applying a 500 W RF electric power (13.56 MHz) to a coilshape electrode at a pressure of 1 Pa. A 100 W RF electric power (13.56MHz) is also applied to the substrate side (test piece stage),effectively applying a negative self-bias voltage. The W film and the Tafilm are both etched on the same order when CF₄ and C1 ₂ are combined.

[0339] Not shown in FIG. 14C, edge portions of the first conductinglayer and the second conducting layer are made into a tapered shape inaccordance with the effect of the bias voltage applied to the substrateside under the above etching conditions by using a suitable resist maskshape. The angle of the tapered portions is from 15 to 45. The etchingtime may be increased by approximately 10 to 20% in order to performetching without any residue remaining on the gate insulating film. Theselectivity of a silicon nitride oxide film with respect to a W film isfrom 2 to 4 (typically 3), and therefore approximately 20 to 50 nm ofthe exposed surface of the silicon nitride film is etched by thisover-etching process. Further, not shown in FIG. 14C, regions of thegate insulating film 406 not covered by first shape conducting layers414 to 417 are made thinner by 20 to 50 nm.

[0340] The first shape conducting layers 414 to 417 (first conductinglayers 414 a to 417 a and second conducting layers 414 b to 417 b) arethus formed from the first conducting layer and the second conductinglayer in accordance with the first etching process.

[0341] A second etching process is performed next, as shown in FIG. 14D.The ICP etching method is similarly used, a mixture of CF₄, Cl₂, and O₂is used as the etching gas, and a plasma is generated by supplying a 500WRF electric power (13.56 MHz) to a coil shape electrode at a pressureof 1 Pa. A 50 W RF (13.56 MHz) electric power is applied to thesubstrate side (test stage), and a self-bias voltage which is lower incomparison to that of the first etching process is applied. The W filmis etched anisotropically under these etching conditions, and Ta (thefirst conducting layers) is anisotropically etched at a slower etchingspeed, forming second shape conducting layers 419 to 422 (firstconducting layers 419 a to 422 a and second conducting layers 419 b to422 b). Further, although not shown in FIG. 14D, the gate insulatingfilm 406 is additionally etched on the order of 20 to 50 nm, becomingthinner, in regions not covered by the second shape conducting layers419 to 422. The masks 409 to 412 are etched by the second etchingprocess, becoming masks 409 a to 412 a.

[0342] The etching reaction of the W film and the Ta film in accordancewith the mixed gas of CF₄ and Cl₂ can be estimated from the radicalsgenerated, and from the ion types and vapor pressures of the reactionproducts. Comparing the vapor pressures of W and Ta fluorides andchlorides, the W fluoride compound WF₆ is extremely high, and the vaporpressures of WCl₅, TaF₅, and TaCl₅ are of similar order. Therefore the Wfilm and the Ta film are both etched by the CF₄ and Cl₂ gas mixture.However, if a suitable quantity of O₂ is added to this gas mixture, CF₄and O₂ react, forming CO and F, and a large amount of F radicals or Fions are generated. As a result, the etching speed of the W film havinga high fluoride vapor pressure becomes fast. On the other hand, even ifF increases, the etching speed of Ta does not relatively increase.Further, Ta easily oxidizes compared to W, and therefore the surface ofTa is oxidized by the addition of O₂. The etching speed of the Ta filmis further reduced because Ta oxides do not react with fluorine andchlorine. It therefore becomes possible to have a difference in etchingspeeds between the W film and the Ta film, and it becomes possible tomake the etching speed of the W film larger than that of the Ta film.

[0343] The masks 409 a to 412 a are removed, and a first doping processis performed as shown in FIG. 15A, adding an impurity element whichimparts n-type conductivity. For example, doping may be performed at anacceleration voltage of 70 to 120 keV and with a dosage of 1×10¹³atoms/cm². The doping process is performed using the second shapeconducting layers 419 to 422 as masks against the impurity element, andso as to also add the impurity element in regions below the secondconducting layers 419 a to 422 a. First impurity regions 425 to 428,which overlap with the second conducting layers 419 a to 422 a, andsecond impurity regions 429 to 432, which have a higher impurityconcentration than the first impurity regions, are thus formed. Notethat the n-type conductivity imparting element is added after removingthe masks 409 a to 412 a in Embodiment 6, but the present invention isnot limited to this. The impurity element which imparts n-typeconductivity may also be added in the step of FIG. 15A, and then themasks 409 a to 412 a may be removed.

[0344] A mask 433 is next formed on the semiconductor layer 404 so as tocover the second conducting layers 421 a and 421 b. The mask 433partially overlaps with the second impurity region 431, sandwiching thegate insulating film 406. A second doping process is then performed, andan impurity element which imparts n-type conductivity is added. Dopingof the n-type conductivity imparting impurity element is performed atconditions in which the dosage is raised higher than that of the firstdoping process, and at a low acceleration voltage. (See FIG. 15B.) Thedoping can be carried out by ion doping or ion implantation. Ion dopingis performed under conditions of a dose amount from 1×10¹³ to 5×10¹²atoms/cm² and an acceleration voltage of 60 to 100 keV. A periodic tablegroup 15 element, typically phosphorous (P) or arsenic (As) is used asthe impurity element which imparts n-type conductivity, and phosphorous(P) is used here. The second conducting layers 419 to 422 become maskswith respect to the n-type conductivity imparting impurity element inthis case, and source regions 434 to 437, drain regions 438 to 441, andLov regions 442 to 445 are formed in a self-aligning manner. Further,Loff region 446 is formed in accordance with the mask 433. The impurityelement which imparts n-type conductivity is added to the source regions434 to 437, and to the drain regions 438 to 441 with a concentration inthe range of 1×10²⁰ to 1×10²¹ atoms/cm³.

[0345] It is possible to freely set the length of the Loff region 446 bycontrolling the size of the mask 433 according to Embodiment 6.

[0346] Note that in the specification, the LDD region overlapping with agate electrode through a gate insulating film is referred to as an Lovregion, and the LDD region not overlapping with a gate electrode througha gate insulating film is referred to as an Loff region.

[0347] The impurity element which imparts n-type conductivity is addedat a concentration of 1×10¹⁷ to 1×10¹⁹ atoms/cm³ in the Loff region, andat a concentration of 1×10¹⁶ to 1×10¹⁸ atoms/cm³ in the Lov region.

[0348] Note that, in FIG. 15B, either before or after doping of animpurity element which imparts n-type conductivity is performed at theabove stated conditions, doping of an n-type conductivity impartingimpurity element may also be performed with an acceleration voltage of70 to 120 keV in a state in which the mask 433 is formed on thesemiconductor layer 404. The concentration of the n-type conductivityimparting impurity element in a portion 446 which becomes an Loff regionof the switching TFT can be suppressed in accordance with the aboveprocess, and the concentration of the n-type conductivity impartingimpurity element in portions 442 and 443, which become Lov regions ofthe TFTs used in the driver circuit can be increased. It is possible tolower the off current of the switching TFT by suppressing theconcentration of the n-type conductivity imparting impurity element inthe portion 446 which becomes the Loff region of the switching TFT.Further, hot carriers generated in accordance with a high electric fieldin the vicinity of the drain and a cause of a degradation phenomenon dueto the hot carrier effect can be prevented by increasing theconcentration of the n-type conductivity imparting impurity element inthe portion 443 which becomes the Lov region of the n-channel TFT usedin the driver circuit.

[0349] After removing the mask 433, source regions 447 and 448, drainregions 449 and 450, and Lov regions 451 and 452, into which an impurityelement having a conductivity type which is the inverse of the above oneconductivity type, are then formed in the semiconductor layers 402 and405 for forming the p-channel TFT, as shown in FIG. 15C. The secondshape conducting layers 419 and 422 are used as a mask with respect tothe impurity element, and the impurity regions are formed in aself-aligning manner. The semiconductor layers 403 and 404, which formn-channel TFTs, are covered over their entire surface areas by a resistmasks 453 at this point. Phosphorous is added in differing concentrationto the source regions 447 and 448, the drain regions 449 and 450, andthe Lov regions 451 and 452, and ion doping is performed here usingdiborane (B₂H₆), so that impurity is added to each of the regions with aconcentration of 2×10²⁰ to 2×10²¹ atoms/cm³.

[0350] Impurity regions (source regions, drain regions, Lov regions, andLoff regions) are formed in the respective semiconductor layers 402 to405 by the above processes. The second conducting layers 419 to 422overlapping the semiconductor layers function as gate electrodes.

[0351] A process of activating the impurity elements added to therespective semiconductor layers is then performed, with the aim ofcontrolling conductivity type. Thermal annealing using an annealingfurnace is performed for this process. In addition, laser annealing andrapid thermal annealing (RTA) can also be applied. Thermal annealing isperformed with an oxygen concentration equal to or less than 1 ppm,preferably equal to or less than 0.1 ppm, in a nitrogen atmosphere at400 to 700° C., typically between 500 and 600° C. Heat treatment isperformed for 4 hours at 500° C. in Embodiment 6. However, for cases inwhich the wiring material used in the conducting layers 419 to 422 isweak with respect to heat, it is preferable to perform activation afterforming an interlayer insulating film (having silicon as its mainconstituent) in order to protect the wirings and the like.

[0352] In addition, heat treatment is performed for 1 to 12 hours at 300to 450° C. in an atmosphere containing between 3 and 100% hydrogen,performing hydrogenation of the semiconductor layers. This process isone of terminating dangling bonds in the semiconductor layers byhydrogen which is thermally excited. Plasma hydrogenation (usinghydrogen excited by a plasma) may also be performed as another means ofhydrogenation.

[0353] A first interlayer insulating film 455 is formed next from asilicon nitride oxide film having a thickness of 100 to 200 nm. (FIG.16A) A second interlayer insulating film 458 made from an organicinsulating material is then formed on the first interlayer insulatingfilm 455.

[0354] Contact holes are then formed in the gate insulating film 406,the first interlayer insulating film 455 and the second interlayerinsulating film 458, and source wirings 459 to 462 are formed to contactthe source regions 447, 435, 436, and 448 through the contact holes. Inthe same way, drain wirings 463 to 465 are further formed to contact thedrain regions 449, 439, 440 and 450. (FIG. 16B)

[0355] Note that it is preferable to form the contact holes by dryetching using CF₄ and O₂ when the gate insulating film 406, the firstinterlayer insulating film 455, and the second interlayer insulatingfilm 458 are SiO₂ films or SiON films. Further, for cases in which thegate insulating film 406, the first interlayer insulating film 455, andthe second interlayer insulating film 458 are organic resin films, it ispreferable to form the contact holes by dry etching using CHF³ or by BHF(buffered hydrogen fluoride, HF+NH₄F). In addition, if the gateinsulating film 406, the first interlayer insulating film 455 and thesecond interlayer insulating film 458 are formed by different materials,it is preferable to change the method of etching and the etchant oretching gas type for each film. The contact holes may also be formed byusing the same etching method and the same etchant or etching gas.

[0356] A third interlayer insulating film 467 is formed next from anorganic resin. Organic resins such as polyimide, polyamide, acrylic, andBCB (benzocyclobutene) can be used. In particular, it is preferable touse acrylic, which has superior levelness, because the third interlayerinsulating film 467 is formed with a strong implication of leveling. Anacrylic film is formed in Embodiment 6 at a film thickness at whichsteps formed by the TFTs can be sufficiently leveled. The film thicknessis preferably from 1 to 5 μm (more preferably between 2 and 4 m).

[0357] A contact hole for reaching the drain wiring 465 is formed nextin the third interlayer insulating film 467, and a pixel electrode 468is formed. An indium oxide tin oxide (ITO) film is formed with athickness of 110 nm in Embodiment 6, and patterning is then performed,forming the pixel electrode 468. Further, a transparent conducting filmin which between 2 and 20% zinc oxide (ZnO) is mixed with indium oxidemay also be used. The pixel electrode 468 becomes an anode of an ELelement. (See FIG. 16C.)

[0358] A first bank 469 and a second bank 470 are formed next from aresin material. The first bank 469 and the second bank 470 are formed inorder to separate EL layers and cathodes, which are formed later, ofadjacent pixels. It is therefore preferable that the second bank 470stick out farther horizontally than the first bank 469. Note that it ispreferable that the combined thickness of the first bank 469 and thesecond bank 470 be made on the order of 1 to 2 μm, but there are nolimitations on this thickness provided that the EL layers and thecathodes formed later of adjacent pixels can be separated. Further, itis necessary to form the first bank 469 and the second bank 470 by aninsulating film, and it is therefore possible to use materials such asan oxide or a resin, for example. The first bank 469 and the second bank470 may both be formed by the same material, and they may also be formedby different materials. The first bank 469 and the second bank 470 areformed in stripe shapes between pixels. The first bank 469 and thesecond bank 470 may be formed on and along the source wirings (sourcesignal lines), and may be formed on and along the gate wirings (gatesignal lines). Note that the first bank 469 and the second bank 470 mayalso be formed by a material in which a pigment is mixed into a resin.(See FIG. 17A.)

[0359] An EL layer 471 and a cathode (MgAg electrode) 472 are formednext in succession without exposure to the atmosphere using vacuumevaporation. Note that the film thickness of the EL layer 471 may befrom 80 to 200 nm (typically between 100 and 120 nm), and that the filmthickness of the cathode 472 may be from 180 to 300 nm (typicallybetween 200 and 250 nm). Note also that, although only one pixel isshown in Embodiment 6, an EL layer which emits red color light, an ELlayer which emits green color light, and an EL layer which emits bluecolor light are formed at the same time at this point. Note thatmaterials to form an EL layer and a cathode is partially laminated onthe bank 470, however, in this specification, the materials are notincluded in the EL layer 471 and the cathode 472.

[0360] The EL layers 471 are formed in order for a pixel correspondingto the color red, a pixel corresponding to the color green, and a pixelcorresponding to the color blue. However, the EL layers 471 lacksresistance with respect to solutions, and therefore each color must beformed separately without using a photolithography technique. It ispreferable to use a metal mask and cover the pixels other than thedesired pixel, and selectively form the EL layers 471 in only therequired locations.

[0361] Namely, first a mask is set so as to cover all of the pixelsexcept for those corresponding to the color red, and red colorlight-emitting EL layers are selectively formed using the mask. Next, amask is set so as to cover all of the pixels except for thosecorresponding to the color green, and green color light-emitting ELlayers are selectively formed using the mask. Finally, a mask is set soas to cover all of the pixels except for those corresponding to thecolor blue, and blue color light-emitting EL layers are selectivelyformed using the mask. Note that, although the use of all differentmasks is described here, the same mask may also be reused. Further, itis preferable to perform processing until all pixel EL layers are formedwithout releasing the vacuum.

[0362] Note that a single layer structure composed of only alight-emitting layer is shown in Embodiment 6 for the EL layer 471, buta structure having layers such as a hole transporting layer, a holeinjecting layer, an electron transporting layer, and an electroninjecting layer in addition to the light-emitting layer may also be usedfor the EL layer. Various examples of these types of combinations havealready been reported, and all such structures may be used. A knownmaterial can be used as the EL layer 471. Considering the EL elementdriver voltage, it is preferable to use an organic material as the knownmaterial.

[0363] The cathode 472 is formed next. An example of using an MgAgelectrode as the cathode is shown in Embodiment 6, but it is alsopossible to use other known materials.

[0364] The TFT substrate having the structure as shown in FIG. 17B isthus completed. Note that, after forming the first bank 469 and thesecond bank 470, it is effective to perform processing in successionwithout exposure to the atmosphere up through to the formation of thecathode 472 by using a multi-chamber method (or an in-line method) thinfilm formation apparatus.

[0365] In Embodiment 6, a source region 504, a drain region 505, an Loffregion 506, an Lov region 507, and a channel forming region 508 arecontained in a semiconductor layer of a switching TFT 501. The Loffregion 506 is formed so as not to overlap with the gate electrode 421through the gate insulating film 406. Further, the Lov region 507 isformed so as to overlap with the gate electrode 421 through the gateinsulating film 406. This type of structure is extremely effective inreducing the off current.

[0366] Further, a single gate structure is used as the switching TFT 501in Embodiment 6, but the present invention may also have a double gatestructure or another type of multi-gate structure for the switching TFT.Two TFTs are substantially connected in series by using the double gatestructure, giving the advantage of additionally reducing the offcurrent.

[0367] Further, the switching TFT 501 is an n-channel TFT in Embodiment6, but a p-channel TFT may also be used.

[0368] A semiconductor layer of an EL driving TFT 502 contains a sourceregion 510, a drain region 511, an Lov region 512, and a channel formingregion 513. The Lov region 512 is formed so as to overlap with the gateelectrode 422 through the gate insulating film 406. Note that the ELdriving TET 502 does not have the Loff region in Embodiment 6, but astructure having the Loff region may also be used.

[0369] Further, the EL driving TFT 502 is a p-channel TFT in Embodiment6, but it may also be an n-channel TFT.

[0370] Note that the active matrix substrate of Embodiment 6 shows anextremely high reliability, and its operational characteristics are alsoincreased, by arranging optimally structured TFT in not only the pixelportion, but also in the driver circuit portion.

[0371] First, a TFT having a structure in which hot carrier injection isreduced so as not to have a very large drop in operational speed is usedas an n-channel TFT 503 of a CMOS circuit forming the driver circuitportion. Note that circuits such as a shift register, a buffer, a levelshifter, and a sampling circuit (sample and hold circuits) are includedas the driver circuits here. Signal conversion circuits such as a D/Aconverter can also be included in the case of performing digital drive.

[0372] A semiconductor layer of the n-channel TFT 503 of the CMOScircuit in Embodiment 6 contains a source region 521, a drain region522, an Lov region 523, and a channel forming region 524.

[0373] Further, it is not necessary to be concerned with the off currentfor the n-channel TFT 203, and importance may be placed more on theoperation speed than the off current. The formation of the Lov region223 overlapping the gate electrode 120 through the gate insulating film106 is therefore effective in increasing the operating speed because theresistance components are reduced as much as possible.

[0374] Further, a semiconductor layer of a p-channel TFT 504 of the CMOScircuit contains a source region 531, a drain region 532, an Lov region533, and a channel forming region 534.

[0375] Note that, in practice, it is preferable to perform packaging(sealing) by a protecting film having high airtight characteristics andlittle outgassing (such as a laminate film or an ultraviolet hardenedresin film) or by a transparent sealing material after completing upthrough to the processes of FIG. 17B so as to have no exposure to theatmosphere. Further, if an inert gas is placed in the inside of thesealing material, and a drying agent (barium oxide, for example) isarranged on the inside of the sealing material, then the reliability ofthe EL element is increased.

[0376] Further, a connector (flexible printed circuit, FPC) is attachedin order to connect the elements formed on the substrate, with terminalsextended from the circuits, to external signal terminals afterincreasing the airtight characteristics in accordance with the packagingprocess or the like. A manufactured product is thus completed. This typeof deliverable state is referred to as an EL display device throughoutthis specification.

[0377] The widths of the gate electrodes in the direction of the channellength differ as stated above in accordance with manufacturing processesof the present invention. Therefore, it is possible to make the ionimplantation within the semiconductor layers arranged under the firstgate electrode less than the ion concentration within the semiconductorlayers not arranged under the first gate electrode by utilizing thedifference in ion penetration depth, due to the difference of gateelectrode thickness, when performing ion injection using the gateelectrodes as masks.

[0378] Further, in order to form the Loff regions using a mask, only thewidth of Lov region needs to be controlled by etching. It becomes easyto control positions of the Lov regions and the Loff regions.

[0379] Note that although an example in which light emitted from the ELlayer is directed toward the substrate side is explained in Embodiment6, the present invention is not limited to this, and a structure inwhich light emitted from the EL layer is directed above the substratemay also be used. In this case, the cathode of the EL element becomesthe pixel electrode, and it is preferable that the EL driving TFT be ann-channel TFT.

[0380] The method of manufacturing an EL display device of the presentinvention is not limited to the manufacturing method described inEmbodiment 6, and other manufacturing methods can be utilized.

[0381] Note that it is possible to freely combine Embodiment 6 with anyof Embodiments 1 to 5.

[0382] Embodiment 7

[0383] An example in which a portable information terminal of thepresent invention has a touch panel is explained in Embodiment 7.

[0384] Reference numeral 1701 in FIG. 18A denotes a display portion of aportable information terminal of the present invention, referencenumeral 1702 denotes a touch panel, and reference numeral 1703 denotes atouch pen. The touch panel 1702 has light transmitting characteristics,and light emitted from the display portion 1701 and light irradiated tothe display portion 1701 can pass through the touch panel 1702. In acase an image is displayed on the display portion 1701 it is possiblefor an operator to see an image on the display portion 1701.

[0385] A detailed structure of the touch panel 1702 is shown in FIG.18B. A plurality of rectangular strip shape first resistive films 1704aligned in a column direction, and a plurality of rectangular stripshape second resistive films 1705 aligned in a row direction, are formedso as to overlap while possessing a predetermined gap in the touch panel1702. The first resistive films 1704 and the second resistive films 1705are formed by ITO.

[0386] Differing voltages are applied to both ends of the firstresistive films 1704 aligned in the column direction, and a voltagegradient is formed in the column direction in portions within the firstresistive films 1704. Differing voltages are also applied to both endsof the second resistive films 1705 aligned in the row direction, and avoltage gradient is formed in the row direction in portions within thesecond resistive films 1705.

[0387] By applying a pressure on the surface of the touch panel 1702 byusing a means such as the touch pen, one of the first resistive films1704 and one of the second resistive films 1705 are contacted. A voltageis generated corresponding to the position contacted, and by measuringthe voltage, information on the position of the first resistive films1704 and the second resistive films 1705 contacted can be written in tothe portable information terminal as electronic data.

[0388] The portable information terminal of the present invention candisplay an image written in to the display portion 1701 and can write ina taken in image by the touch pen 1703 with the above structure.

[0389] Note that it is possible to freely combine Embodiment 7 with anyof Embodiments 1 to 6.

[0390] Embodiment 8

[0391] An example in which a display portion of a portable informationterminal of the present invention functions as an area sensor isexplained in Embodiment 8. A structure of the display portion ofEmbodiment 8 is explained in detail below. FIG. 19 shows a circuitdiagram of a display portion of this embodiment.

[0392] Source signal lines S1 to Sx, electric power source supply linesV1 to Vx, gate signal lines G1 to Gy, reset gate signal lines RG1 toRGy, sensor gate signal lines SG1 to SGy, sensor output wirings SS1 toSSx, and a sensor electric power source line VB are formed in a displayportion 901.

[0393] The display portion 901 has a plurality of pixels 902. The pixels902 have one of the source signal lines S1 to Sx, one of the electricpower source supply lines V1 to Vx, one of the gate signal lines G1 toGy, one of the reset gate signal lines RG1 to RGy, one of the sensorgate signal lines SG1 to SGy, one of the sensor output wirings SS1 toSSx, and the sensor electric power source line VB.

[0394] The sensor output wirings SS1 to SSx are connected to constantelectric current power supplies 903_1 to 903_x, respectively.

[0395] A detailed structure of the pixel 902 is shown in FIG. 20. Aregion enclosed by a dotted line is the pixel 902. Note that a sourcesignal line S denotes one of the source signal lines S1 to Sx. Further,an electric power source supply line V denotes one of the electric powersource supply lines V1 to Vx. A gate signal line G denotes one of thegate signal lines G1 to Gy, and a reset gate signal line RG denotes oneof the reset gate signal lines RG1 to RGy. In addition, a sensor gatesignal line SG denotes one of the sensor gate signal lines SG1 to SGy,and a sensor output wiring SS denotes one of the sensor output wiringsSS1 to SSx.

[0396] The pixel 902 has a switching TFT 904, an EL driver TFT 905, andan EL element 906. Further, in FIG. 20 a capacitor 907 is formed in thepixel 902, but the capacitor 907 need not be formed.

[0397] A gate electrode of the switching TFT 904 is connected to thegate signal line G. One of a source region and a drain region of theswitching TFF 904 is connected to the source signal line S, and theother is connected to a gate electrode of the EL driver TFT 905.

[0398] The source region of the EL driver TFT 905 is connected to theelectric power source supply line V, and the drain region of the ELdriver TFT 905 is connected to the EL element 906. The capacitor 907 isformed connected to the gate electrode of the EL driver TFT 905 and tothe electric power source supply line V.

[0399] The EL element 906 is composed of an anode, a cathode, and an ELlayer formed between the anode and the cathode. When the anode isconnected to a drain region of the EL driver TFT 905, the anode becomesa pixel electrode and the cathode becomes an opposing electrode.Conversely, when the cathode is connected to a drain region of the ELdriver TFT 905, the anode becomes the opposing electrode and the cathodebecomes the pixel electrode.

[0400] In addition, the pixel 902 has a reset TFT 910, a buffer TFT 911,a selection TFT 912, and a photodiode 913.

[0401] A gate electrode of the reset TFT 910 is connected to the resetgate signal line RG. A source region of the reset TFT 910 is connectedto the sensor electric power source line VB, and the sensor electricpower source line VB is always maintained at a constant electricpotential (standard electric potential). Further, a drain region of thereset TFT 910 is connected to the photodiode 913 and to a gate electrodeof the buffer TFT 911.

[0402] Although not shown in the figure, the photodiode 913 has acathode, an anode, and a photoelectric conversion layer formed betweenthe cathode electrode and the anode electrode. The drain region of thereset TFT 910 is connected specifically to the anode electrode or thecathode electrode of the photodiode 913.

[0403] A drain region of the buffer TFT 911 is connected to the sensorelectric power source line VB, and is always maintained at the standardelectric potential. A source region of the buffer TFT 911 is connectedto a source region or a drain region of the selection TFT 912.

[0404] A gate electrode of the selection TFT 912 is connected to thesensor gate signal line SG. One of a source region and a drain region ofthe selection TFT 912 is connected to the source region of the bufferTFT 911, as stated above, and the other is connected to the sensoroutput wiring SS. The sensor output wiring SS is connected to a constantelectric current power source 903 (one of the constant electric currentpower sources 903_1 to 903_x), and a constant electric always flows.

[0405] An explanation of a method of driving the display portion ofEmbodiment 8 is explained next using FIGS. 19 and 20.

[0406] The EL element 906 of the pixel 902 functions as a light sourceof the area sensor, and the switching TFT 904 and the EL driver TFT 905control the operation of the EL element 906 as the light source.

[0407] Light emitted from the EL element is reflected by the subject andis irradiated to the photodiode 913 of the pixel 902. The photodiode 913converts the irradiated light to an electrical signal having imageinformation. The electrical signal having image information which isgenerated by the photodiode 913 is then taken in within the portableinformation terminal as an image signal by the buffer TFT 911 and theselection TFT 912.

[0408] The reset TFT 910, the buffer TFT 911, and the selection TFT 912may be either an n-channel TFT or a p-channel TFT in Embodiment 8.However, it is preferable that the reset TFT 910 and the buffer TFT 911have opposite polarities.

[0409] First, the reset TFTs 910 of a first line of pixels connected tothe reset gate signal line RG1 are placed in an ON state in accordancewith a reset signal input to the reset gate signal line RG1. Thestandard electric potential of the sensor electric power source line VBis therefore applied to the gate electrode of the buffer TFT 911.

[0410] Further, the selection TFTs 912 of a first line of pixelsconnected to the sensor gate signal line SG1 are placed in an OFF statein accordance with a sensor signal input to the sensor gate signal lineSG1. The source region of the buffer TFT 911 is therefore maintained atan electric potential in which an electric potential difference VGsbetween the source region and the gate electrode of the buffer TFT 911is subtracted from the standard electric potential. Note that a periodduring which the reset TFT 910 is in an ON state is referred to as areset period in this embodiment.

[0411] The electric potential of the reset signal input to the resetgate signal line RG1 is then changed, and all of the reset TFTs 910 ofthe first line of pixels are placed in an OFF state. The standardelectric potential of the sensor electric power source line VB istherefore no longer applied to the gate electrodes of the buffer TFTs911 of the first line of pixels. Note that a period during which thereset TFT 910 is in an OFF state is referred to as a sample period ST inthis embodiment. In particular, a period during which the reset TFTs 910of the first line of pixels is in an OFF state is referred to as asample period ST1.

[0412] The electric potential of the sensor signal input to the sensorgate signal line SG1 changes in the sample period ST1, and the selectionTFTs 912 of the first line of pixels are placed in an ON state. Thesource regions of the buffer TFTs 911 of the first line of pixels aretherefore electrically connected to the sensor output wiring SS1,through the selection TFTs 912. The sensor output wiring SS1 isconnected to the constant electric current power source 903_1, andtherefore the buffer TFTs 911 function as source followers, and theelectric potential difference VGS between the source region and the gateelectrode is constant.

[0413] An electric current flows in the photodiode 913 in the sampleperiod ST1 when light from the EL element 906 is reflected by a subjectand is irradiated to the photodiode 913. The electric potential of thegate electrode of the buffer TFT 911, maintained at the standardelectric potential during the reset period, therefore changes incorrespondence with the amount of electric current which develops in thephotodiode 913.

[0414] The electric current flowing in the photodiode 913 isproportional to the strength of the light irradiated to the photodiode913, and therefore the image of the subject is converted as is in thephotodiode 913 into an electrical signal. The electrical signalgenerated in the photodiode 913 is input to the gate electrode of thebuffer TFT 911.

[0415] The electric potential difference VGS between the source regionand the gate electrode of the buffer TFT 911 is always constant, andtherefore the source region of the buffer TFT 911 maintains an electricpotential in which VGS is subtracted from the electric potential of thegate electrode of the buffer TFT 911. Therefore, if the electricpotential of the gate electrode of the buffer TFT 911 changes, theelectric potential of the source region of the buffer TFT 911 alsochanges in accompaniment.

[0416] The electric potential of the source region of the buffer TFT 911is input to the sensor output wiring SS1, through the selection TFT 912,as an image signal.

[0417] Next, the reset TFTs 910 of the first line of pixels connected tothe reset gate signal line RG1 are placed in an ON state in accordancewith the reset signal input to the reset gate signal line RG1, and thereset period again begins. The reset TFTs 910 of a second line of pixelsconnected to the reset gate signal line RG2 are also simultaneouslyplaced in an ON state in accordance with the reset signal input to thereset gate signal line RG2, and a sampling period ST2 begins.

[0418] An electrical signal having image information is generated in thephotodiode in the sampling period ST2, similar to what occurs in thesampling period ST1, and the image signal is input to the sensor outputwiring SS2.

[0419] If the above operations are repeated, one image can be read in asan image signal when the sampling period STy is complete. Note that aperiod up through the appearance of all of the sampling periods ST1 toSTy is referred to as a sensor frame period SF in this specification.

[0420] Further, it is necessary to always emit light from the ELelements of each pixel in each sampling period. For example, it is atleast necessary for the EL elements of the first line of pixels to emitlight during the sampling period ST1. Note that all of the pixels mayalways emit light during the sensor frame SF.

[0421] Note also that for a case of an area sensor into which a colorimage is written, the display portion has pixels corresponding to eachof the colors R (red), G (green), and B (blue). The pixels correspondingto each of the colors RGB have three types of EL elements correspondingto RGB, or have white color light emitting EL elements and three typesof color filters for RGB, or have blue color or blue-green color lightemitting EL elements and a fluorescing body (fluorescing colorconversion layer, CCM).

[0422] Each color of RGB light emitted from the pixels corresponding toeach of the RGB colors is irradiated to the subject in order. Then eachof the RGB colors of light reflected by the subject is irradiated to thephotodiodes of the pixels, and image signals corresponding to each ofthe RGB colors are taken in to the area sensor.

[0423] It is possible for the display portion to function as an areasensor with the portable information terminal of Embodiment 8. It istherefore possible to display an image, read in by the display portion,in the display portion, to confirm the read in image on the spot, and itis possible to send the image to another person as data.

[0424] Note that it is possible to freely combine Embodiment 8 with anyof Embodiments 1 to 7.

[0425] An additionally detailed cross sectional structure of the displayportion is shown in FIG. 22 here, a top surface structure is shown inFIG. 23A and a circuit diagram is shown in FIG. 23B. FIGS. 22, 23A, and23B use common reference symbols and therefore may be mutuallyreferenced.

[0426] A switching TFT 4402 formed on a substrate 4401 in FIG. 22 is ann-channel TFT formed by using a known method. Further, a wiring denotedby reference numeral 4403 is a gate wiring electrically connected togate electrodes 4404 a and 4404 b of the switching TFT 4402. Note that,although a double gate structure in which two channel forming regionsare formed is used in Embodiment 9, a single gate structure in which onechannel forming region is formed, and a triple gate structure in whichthree channel forming regions are formed, may also be used.

[0427] Further, a drain wiring 4405 of the switching TFT 4402 iselectrically connected to a gate electrode 4407 of an EL driver TFT4406. Note that the EL driver TFT 4406 is a p-channel TFT formed byusing a known method. Note also that, although a single gate structureis used in Embodiment 9, a double gate structure and a triple gatestructure may also be used.

[0428] A first passivation film 4408 is formed on the switching TFT 4402and on the EL driver TFT 4406, and a leveling film 4409 made from aresin is formed on the first passivation film. Leveling of steps due tothe TFTs by using the leveling film 4409 is extremely important. An ELlayer subsequently formed is extremely thin, and therefore lightemission irregularities may be caused by the existence of a step. It isthus preferable to perform leveling before forming a pixel electrode soas to be able to form the EL layer with a surface that is as level aspossible.

[0429] Furthermore, reference numeral 4410 denotes a pixel electrode (ELelement anode) made from a transparent conducting film, and the pixelelectrode is electrically connected to a drain wiring 4417 of the ELdriver TFT 4406. A chemical compound of indium oxide and tin oxide, achemical compound of indium oxide and zinc oxide, zinc oxide, tin oxide,and indium oxide can be used as the transparent conducting film.Further, a film in which gallium is added to the above films may also beused as a transparent conducting film.

[0430] An EL layer 4411 is formed on the pixel electrode 4410. Notethat, although only one pixel is shown in FIG. 22, the EL layer isdivided up and formed corresponding to the colors or R (red), G (green),and B (blue) in Embodiment 9. Further, a low molecular weight organic ELmaterial may be formed by an evaporation method in Embodiment 9.Specifically, a lamination structure may be formed in which a 20 nmthick copper phthalocyanine (CuPc) film is formed as a hole injectinglayer, and a 70 nm thick tris-8-aluminum quinolinolate complex (Alq₃)film may be formed on the CuPc film as a light emitting layer. The colorof light emitted can be controlled by adding a fluorescing pigment suchas quinacridon. perillin, and DCM1 to Alq3.

[0431] Note that the above example is one example of organic ELmaterials capable of being used as the EL layer, and the EL layer neednot be limited to these. An EL layer in which a light emitting layer, acharge transporting layer, and a charge injecting layer are freelycombined (layers for emitting light and for performing transport ofcarriers for light emission) may also be used. For example, an exampleof using low molecular weight organic EL materials as the EL layer isshown in Embodiment 9, but high molecular weight EL materials may alsobe used. Further, it is also possible to use inorganic materials such assilicon carbide as charge transporting layers and charge injectinglayers. Known materials can be used for these organic EL materials andinorganic materials.

[0432] A cathode 4412 made from a conducting film is formed next on theEL layer 4411. An alloy film of aluminum and lithium is used as theconducting film in the case of Embodiment 9. Of course, a known MgAgfilm (an alloy film of magnesium and silver) may also be used. Aconducting film made from an element residing in group 1 or group 2 ofthe periodic table, or a conducting film to which one of the aboveelements is added, may be used as the cathode material.

[0433] An EL element 4413 is completed at the point where the cathode4412 is formed. Note that the EL element 4413 indicates a capacitorformed by the pixel electrode (anode) 4410, the EL layer 4411, and thecathode 4412 here.

[0434] A top surface structure of the pixel in Embodiment 9 is explainedusing FIG. 23A. A source region of the switching TFT 4402 is connectedto a source signal line 4415 containing a source wiring, and a drainregion of the switching TFT 4402 is connected to the drain wiring 4405.Further, the drain wiring 4405 is electrically connected to the gateelectrode 4407 of the EL driver TFT 4406. A source region of the ELdriver TFT 4406 is electrically connected to an electric power sourcesupply line 4416, and a drain region of the EL driver TFT 4406 iselectrically connected to a drain wiring 4417. Furthermore, the drainwiring 4417 is electrically connected to a pixel electrode (anode) 4418shown by a dotted line.

[0435] A storage capacitor is formed at this point in a region denotedby reference numeral 4419. The storage capacitor 4419 is formed inbetween a semiconductor film 4420 electrically connected to the electricpower source supply line 4416, an insulating film (not shown in thefigures) formed on the same layer as a gate insulating film, and thegate electrode 4407. Furthermore, it is also possible to use acapacitance formed by the gate electrode 4407, a layer (not shown in thefigures) which is the same as a first interlayer insulating film, andthe electric power source supply line 4416 as a storage capacitor.

[0436] Embodiment 9

[0437] An example of fabricating an EL display device using the presentinvention will be explained in embodiment 9. Note that FIG. 21A is a topview of an EL display device using the present invention, and FIG. 21Bis a cross sectional view thereof.

[0438] In FIG. 21A and FIG. 21B, reference numeral 4001 denotes asubstrate, 4002 denotes a display portion, 4003 denotes a source sidedriving circuit, 4004 denotes a gate side driving circuit. The drivingcircuits are connected to external equipment, through an FPC (flexibleprinted circuit) 4006 via a wiring 4005.

[0439] At this time, a first sealing material 4101, a covering material4102, a filler material 4103 and a second sealing material 4104 areprovided so as to enclose the display portion 4002, source side drivingcircuit 4003, and gate side driving circuit 4004.

[0440] A cross sectional diagram of FIG. 21A cut along the line A-A′ isshown in FIG. 21B. On the substrate 4001, a driver TFT 4201 included inthe source side driving circuit 4003 (an n-channel TFT and a p-channelTFT are shown here) and an EL driving TFT 4202 included in the pixelportion 4002 (a TFT for controlling the current flowing to an EL elementis shown here) are formed.

[0441] In this embodiment, a p-channel TFT and an n-channel TFTfabricated by a known method are used for the driving TFT 4201 and ap-channel TFT fabricated by a known method used for an EL driving TFT4202. Further the display portion 4002 is provided the storage capacitor(not shown in figure) connected gate electrode of the EL driving TFT4202.

[0442] An interlayer insulating film (leveling film) 4301 made from aresin material is formed on the driver TFT 4201 and the pixel TFT 4202,and a pixel electrode (anode) 4302 electrically connected to a drain ofthe pixel TFT 4202 thereon. The pixel electrode 4302 is formed from atransparent conductive film having large work function. As thetransparent conductive film, an indium oxide and tin oxide compound oran indium oxide and zinc oxide compound can be utilized. The transparentconductive film doped with gallium also can be used.

[0443] Then, an insulating film 4303 is formed on the pixel electrode4302, and an opening portion is formed on the pixel electrode 4302. Atthe opening portion, an EL (electro-luminescence) layer 4304 is formedon the pixel electrode 4302. A known organic EL material or inorganic ELmaterial is used as the EL layer 4304. Both of low molecular type(monomer based) organic EL materials and high molecular type (polymerbased) organic EL materials can be used as the organic materials.

[0444] A known evaporation of painting technique may be used to form theEL layer 4304. The EL layer may have a lamination structure by freelycombining a hole injecting layer, a hole transporting layer, a lightemitting layer, an electron transporting layer, and an electroninjecting layer, or a single layer structure.

[0445] On the EL layer 4304, a cathode 4305 made of a conductive filmhaving a light-shielding property (typically, a conductive filmcomprising aluminum, cupper, or silver as a main component, or alamination film of those and other conductive film) is formed. It ispreferable to remove as much as possible any moisture or oxygen existingin the interface between the cathode 4305 and the EL layer 4304. It istherefore necessary to use a method of depositing continuously thecathode 4305 and the EL layer 4304 in vacuum or depositing the EL layer4304 in an atmosphere of nitrogen or in a rare gas atmosphere, thereby acathode 4305 is formed without exposing to oxygen and moisture. Theabove film deposition becomes possible in embodiment 9 by using amulti-chamber method (cluster tool method) film deposition apparatus.

[0446] Then, the cathode 4305 is electrically connected to the wiring4005 in the region denoted by reference numeral 4306. The wiring 4005for imparting a predetermined voltage to the cathode 4305 is connectedto the FPC 4006 through an anisotropic conductive material 4307.

[0447] As mentioned above, an EL element is made from the pixelelectrode (anode) 4302, the EL layer 4304 and the cathode 4305. The ELelement is enclosed with a covering material 4102 which is laminatedwith the substrate 4001 through a first sealing material 4101 and asecond sealing material 4104, and sealed with a filer material 4103.

[0448] Materials such as a glass plate, a metal plate (typically, astainless steel plate), a ceramic plate and a plastic material(including a plastic film) can be used as the covering material 4102. Asplastic material an FRP (fiberglass-reinforced plastic) plate, a PVF(polyvinyl fluoride) film, a Mylar film, a polyester film, and anacrylic film can be used. It is preferable to use a sheet structure inwhich aluminum foil is sandwiched by a PVF film or a Mylar film.

[0449] Note that, for a case in which the emission direction of lightemitted from the EL element is directed to the covering material side,it is necessary for the covering material to possess transparency. Inthe case, a transparent material such as a glass plate, a plastic plate,a polyester film or an acrylic film can be used.

[0450] Additionally, a filler material 4103 is formed using ultravioletcuring resin or thermally curable resin. PVC (polyvinyl chloride),acrylic, polyimide, epoxy resin, silicone resin, PVB (polyvinylbutyral), and EVA (ethylene vinyl acetate) can be used as the fillermaterial. If a drying agent (preferably, barium oxide) is formed on theinside of the filler material 4103 or materials which can absorb oxygen,then it can suppress the degradation of the EL element.

[0451] Further, spacer may be contained in the filler material 4103. Atthis time, the spacer is formed by using barium oxide, thereby thespacer itself has a hygroscopic property. Further, in the case ofproviding the spacer, it is effective that a resin film is provided onthe cathode 4305 as a buffer layer for relaxation of pressure from thespacer.

[0452] Further, the wiring 4005 is electrically connected to the FPC4006 via the anisotropic conductive film 4307. The wiring 4005 transmitssignals forwarding the pixel portion 4002, source side driving circuit4003 and gate side driving circuit 4004 to the FPC 4006 and areelectrically connected to external equipment through the FPC 4006.

[0453] Also, in the present embodiment, a second sealing material 4104is provided to cover an exposure portion of the first sealing material4101 and portion of the FPC 4006 to obtain the structure in which the ELelement is completely shut out from the outside. In this way, the ELdisplay device has a cross sectional structure shown in FIG. 21B.

[0454] Embodiment 10

[0455] An EL display device having a pixel structure which differs fromthat of Embodiment 9 is explained in Embodiment 10. FIG. 24 is used inthe explanation. Note that the explanation of Embodiment 9 may bereferred to regarding portions to which reference symbols identical tothose of FIG. 22 are attached.

[0456] An n-channel TFT is formed using a known method as an EL driverTFT 4501 in FIG. 24. A gate electrode 4502 of the EL driver TFT 4501 isof course electrically connected to the drain wiring 4405 of theswitching TFT 4402. Further, a drain wiring 4503 of the EL driver TFT4501 is electrically connected to a pixel electrode 4504.

[0457] The pixel electrode 4504, composed of a conducting film,functions as a cathode of an EL element in Embodiment 10. Specifically,an alloy film of aluminum and lithium is used. However, a conductingfilm made from an element residing in group 1 or group 2 of the periodictable, and a conducting film to which one of the above elements isadded, may also be used.

[0458] An EL layer 4505 is formed on the pixel electrode 4504. Notethat, although only one pixel is shown by FIG. 24, an EL layercorresponding to the color G (green) is formed in Embodiment 10by anevaporation method or an application method (preferably spin coating).Specifically, a lamination structure is used, in which a 20 nm thicklithium fluoride (LiF) film is formed as an electron injecting layer,and a 70 nm thick PPV (polyparaphenylene vinylene) film is formed on theLiF film as a light emitting layer.

[0459] Next, an anode 4506 is formed on the EL layer 4505 from atransparent conducting film. A conducting film composed of a chemicalcompound of indium oxide and tin oxide, or a chemical compound of indiumoxide and zinc oxide, is used as the transparent conducting film in thecase of Embodiment 10.

[0460] An EL element 4507 is completed at the point where the arode 4506is formed. Note that the EL element 4507 referred to here indicates acapacitor formed by the pixel electrode (cathode) 4504, the EL layer4505, and the anode 4506.

[0461] For a case of a high voltage equal to or greater than 10 Vapplied to the EL element, degradation due to the hot carrier effect inthe EL driver TFT 4501 appears. It is effective in this case to use ann-channel TFT, having a structure in which an LDD region 4509 of a drainregion side overlaps with the gate electrode 4502 through the gateinsulating film 4510, as the EL driver TFT 4501.

[0462] Further, the EL driver TFT 4501 of Embodiment 10 forms aparasitic capacitance between the gate electrode 4502 and the LDD region4509 referred to as a gate capacitance. By regulating the gatecapacitance, it can be made to possess a function similar to that of thestorage capacitor 4418 shown in FIGS. 23A and 23B. In particular, thecapacitance of the storage capacitor may be smaller for a case ofoperating the EL display device by a digital driving method than for acase of an analog driving method operation, and therefore the storagecapacitor can be substituted by the gate capacitance.

[0463] Note that for cases in which the voltage applied to the ELelement is 10 V or less, preferably equal to or less than 5 V, there isalmost no problem of degradation due to the above hot carrier effect,and therefore an n-channel TFT having a structure in which the LDDregion 4509 is omitted may also be used in FIG. 24.

[0464] Embodiment 11

[0465] An EL display device of a display portion of a portableinformation terminal of the present invention may also have a structurein which several TFTs are formed within a pixel. For example, 4 to 6 ormore TFTs may be formed. It is possible to implement the presentinvention without placing any limitations on the pixel structure of theEL display device.

[0466] Embodiment 12

[0467] An EL display device used in a display portion of a portableinformation terminal of the present invention is not limited to anactive matrix type, and a passive type may also be used. A crosssectional diagram of a display portion of an EL display device used inEmbodiment 12is shown in FIG. 26.

[0468] Anodes 2602 are formed having a rectangular strip shape inalignment on a substrate 2601. A matrix shape insulating film 2603 isformed on the substrate 2601 covering the anodes 2602. Banks 2604 arethen formed on the insulating film 2603 in order to separate adjacent ELlayers and cathodes.

[0469] It is preferable to use a material having insulatingcharacteristics to form the bank 2604 in order to also electricallyseparate the adjacent EL layers and cathodes.

[0470] EL layers 2605 and cathodes 2607 are then formed and laminated inorder on a passive substrate having the substrate 2601, the anodes 2602,the insulating film 2603, and the banks 2604. The EL layers 2605 and thecathodes 2606 which are adjacent, sandwiching the banks 2604, areseparated by the banks 2604.

[0471] The passive type EL display device has an easier method ofmanufacture, and a lower cost, than the active matrix type EL displaydevice. It is therefore possible to lower the cost of the portableinformation terminal itself by using the passive type EL display devicein the display portion of the portable information terminal of thepresent invention.

[0472] Note that the passive type EL display device used in the displayportion of the portable information terminal of the present invention isnot limited to the structure shown by Embodiment 12. A passive type ELdisplay device used in the display portion of the portable informationterminal of the present invention may have any type of structure.

[0473] It is possible to implement Embodiment 12by freely combining itwith Embodiment 1 or Embodiment 7.

[0474] Embodiment 13

[0475] A structure of a liquid crystal display device of a displayportion of a portable information terminal of the present invention isexplained in Embodiment 13. An example of a schematic diagram of theliquid crystal display device of Embodiment 13is shown in FIG. 27.

[0476] A source signal line driver circuit 1301 and a gate signal linedriver circuit 1302 are a portion of a driver circuit. Source signallines 1303 connected to the source signal line driver circuit 1301, andgate signal lines 1304 connected to the gate signal line driver circuit1302 intersect in a display portion 1308. A pixel thin film transistor(pixel TFT) 1305, a liquid crystal cell 1306 in which a liquid crystalis sandwiched between an opposing electrode and a pixel electrode, and astorage capacitor 1307 are formed in regions having the source signallines 1303 and the gate signal lines 1304.

[0477] An analog video signal (analog signal having image information)input to the source signal lines 1303 is selected by the pixel TFTs 1305and written into predetermined pixel electrodes.

[0478] The analog video signal, sampled by a timing signal output fromthe source signal line driver circuit 1301, is supplied to the sourcesignal lines 1303.

[0479] Switching of corresponding pixel TFTs 1305 is performed inaccordance with a gate signal output from the gate side driver circuit1302, and the liquid crystal of the liquid crystal cells 1306 is drivenin accordance with the analog signal having image information outputform the source signal lines 1303. An image is thus displayed in thedisplay portion.

[0480] Note that the liquid crystal display device used in the displayportion of the portable information terminal of the present invention isnot limited to the structure shown in Embodiment 13. The liquid crystaldisplay device used in the display portion of the portable informationterminal of the present invention may have any type of structure.

[0481] It is possible to implement Embodiment 13by freely combining itwith Embodiment 1 or Embodiment 7.

[0482] Embodiment 14

[0483] EL for formation of an EL layer of an EL element, in an ELdisplay device of a display portion of a portable information terminalof the present invention, is explained.

[0484] It is possible to use all known materials for the EL used in theEL layer of the EL element in the EL display device of the displayportion of the portable information terminal of the present invention.However, it becomes possible to suppress the electric power consumptionof the portable information terminal itself by using in particularmaterials in which the light emission efficiency is very high from amongall known EL materials.

[0485] By utilizing the emission of light when returning to a base statefrom a triplet excitation state (phosphorescence), in addition to theemission of light when returning to a base state from a singletexcitation state (fluorescence), the maximum external quantum efficiencycan be increased. Specifically, it is possible to increase the externalquantum efficiency, approximately 5% for a case of only utilizingfluorescence, to approximately 10% or greater, typically up to 20%, fora case of utilizing phosphorescence in addition to fluorescence. Themaximum value of the strength of emitted light can then be made equal toor greater than 251 m/W, typically approximately 401 m/Wby utilizingphosphorescence in addition to fluorescence, compared to approximately201 m/W for a case of only utilizing fluorescence.

[0486] Materials such as the following can be given as EL materialscapable of utilizing phosphorescence in addition to fluorescence: PtOEP(2,3,7,8,12,13,17,18-octaethyl 21H, 23H-porphine platinum(II)); andIr(ppy)₃ (tris(2-phenylpyridine)iridium).

[0487] An EL element having an EL material with which phosphorescence isalso utilized, in addition to fluorescence, has a higher light emissionefficiency when compared to an EL element having an EL material whichonly utilizes fluorescence, and the power consumption of the portableinformation terminal itself can thus be suppressed. The ease of use ofthe portable information terminal can therefore be made better bysuppressing the power consumption because the portable informationterminal is carried and used by an operator.

[0488] It is possible to implement Embodiment 14 by freely combining itwith any of Embodiments 1 to 12.

[0489] Embodiment 15

[0490] A case of automatically switching the direction of imagesdisplayed in a display portion, or the direction of images such ascharacters, numerals, and symbols displayed in operation keys, inaccordance with an angle θ between a display panel in a connectionportion and an operation portion in a portable information terminal ofthe present invention, is explained in detail in Embodiment 15.

[0491] A cross sectional diagram of a connection portion 801 of aportable information terminal of Embodiment 15 is shown in FIGS. 28A to28C. Reference numeral 802 denotes a display panel, reference numeral803 denotes an operation panel, and both panels are connected in theconnection portion 801. Note that, although an example is shown inEmbodiment 15 in which reference numeral 802 denotes the display paneland reference numeral 803 denotes the operation panel, the presentinvention is not limited to this structure. Conversely, referencenumeral 802 may also denote the operation panel and reference numeral803 may also denote the display panel.

[0492] The display panel 802 is connected to a rotation shaft 804 in theconnection portion 801. A cross section of the rotation shaft 804 has ashape in which a portion of a circle has been removed. This becomes anarc shape in Embodiment 15.

[0493] Further, the operation panel 803 is connected to a rotationportion 805 in the connection portion 801. It is possible to performrotation in the rotation portion 805 with the rotation shaft 804 as amain axis, and the angle θ between the display panel 802 and theoperation panel 803 is determined in accordance with the angle ofrotation of the rotation portion 805.

[0494] A button 806 is formed in the rotation portion 805 in order torecognize the angle θ between the display panel 802 and the operationpanel 803. It is possible to sense the angle θ by whether or not thebutton 806 contacts a portion of the arc or the rotation shaft 804.

[0495] Cross sectional diagrams of the connection portion 801 for casesin which θ=0°, θ=30°, and θ=120° are shown in FIGS. 28A, 28B, and 28C,respectively.

[0496] For example, the rotation shaft 804 contacts the button 806 whenθ=0° in FIG. 28A and when θ=30° in FIG. 28B. The rotation shaft 804 isseparated from the button 806 for the case of θ=120° in FIG. 28C.

[0497] The direction of the image displayed in the display portion, andthe direction of the images such as characters, numerals, and symbolsdisplayed in the operation keys, switch depending upon whether or notthe button 806 contacts the rotation shaft 804. It is possible toautomatically switch the direction of the image displayed in the displayportion, and the direction of the images such as characters, numerals,and symbols displayed in the operation keys, in accordance with theangle θ formed between the display panel and the operation panel in theconnection portion in accordance with the above structure.

[0498] Note that it is possible for a designer to suitably determine thespecific value of the angle θ at which the image direction is switchedby changing the shape of the rotation shaft 804.

[0499] It is possible to implement Embodiment 15 by freely combining itwith any of Embodiments 1 to 14.

[0500] A portable information terminal of the present invention hasoperation keys for inputting characters, symbols, numerals and the like,each with an LED (light emitting diode), an EL display device, or aliquid crystal display device and the like, and by displayingcharacters, symbols, and numerals in the operation keys in accordancewith the LEDs (light emitting diodes), EL display devices, or liquidcrystal display devices, an operator can differentiate between theoperation keys. The operator can even discern the operation keys in adark environment in accordance with the above structure.

[0501] The operator can appropriately change the direction of thedisplay of the EL display device used in the display portion, and canappropriately change the direction of the images such as characters,symbols, and numerals displayed in the operation keys, in accordancewith the portable information terminal usage. The ease of use of theportable information terminal can be increased with the above structure.

[0502] Further, the portable information terminal of the presentinvention may also use a structure having a CCD camera. By using the CCDcamera, the operator can send image information, taken in as electronicdata to the portable image terminal by the CCD camera, to other personson the spot.

What is claimed is:
 1. An electronic device functioning as a telephone,comprising: a display portion; an audio input portion; an audio outputportion; and operation keys; wherein: the display portion has activeelements; the operation keys have LEDs; and the direction of an imagedisplayed by the LEDs is switchable.
 2. An electronic device accordingto claim 1 , wherein the active element has EL or liquid crystals.
 3. Anelectronic device functioning as a telephone, comprising: a displayportion; an audio input portion; an audio output portion; and operationkeys; wherein: the display portion has EL elements; the operation keyshave liquid crystals; and the direction of an image displayed by theliquid crystals is switchable.
 4. An electronic device functioning as atelephone, comprising: a first panel having: one of an audio inputportion and an audio output portion; and a display portion; a secondpanel having: one of an audio input portion and an audio output portion;and operation keys; wherein: the first panel and the second panel areconnected; the angle between the first panel and the second panel can bearbitrarily changed; the display portion has EL elements; the operationkeys have LEDs; and the direction of an image displayed by the LEDs isswitchable.
 5. An electronic device functioning as a telephone,comprising: a first panel having: one of an audio input portion and anaudio output portion; and a display portion; a second panel having: oneof an audio input portion and an audio output portion; and operationkeys; wherein: the first panel and the second panel are connected; theangle between the first panel and the second panel can be arbitrarilychanged; the display portion has EL elements; the operation keys haveliquid crystals; and the direction of an image displayed by the liquidcrystals is switchable.
 6. An electronic device functioning as atelephone, comprising: a first panel having: one of an audio inputportion and an audio output portion; and a display portion; a secondpanel having: one of an audio input portion and an audio output portion;and operation keys; wherein: the display portion has EL elements; theoperation keys have LEDs; the first panel and the second panel areconnected; the angle between the first panel and the second panel can bearbitrarily changed; the direction of an image displayed by the LEDs isswitchable in accordance with the angle between the first panel and thesecond panel.
 7. An electronic device functioning as a telephone,comprising: a first panel having: one of an audio input portion and anaudio output portion; and a display portion; a second panel having: oneof an audio input portion and an audio output portion; and operationkeys; wherein: the display portion has EL elements; the operation keyshave liquid crystals; the first panel and the second panel areconnected; the angle between the first panel and the second panel can bearbitrarily changed; the direction of an image displayed by the liquidcrystals is switchable in accordance with the angle between the firstpanel and the second panel.
 8. An electronic device functioning as atelephone, comprising: a first panel having: one of an audio inputportion and an audio output portion; and a display portion; a secondpanel having: one of an audio input portion and an audio output portion;and operation keys; wherein: the first panel and the second panel areconnected; the angle between the first panel and the second panel can bearbitrarily changed; the display portion has a plurality of pixels; theplurality of pixels each have: a photodiode; an EL element; a switchingTFT; an EL driver TFT; a reset TFT; a buffer TFT; and a selection TFT;the switching TFT and the EL driver TFT control light emission from theEL element; light emitted from the EL elements is reflected upon asubject and irradiated onto the photodiodes; the photodiodes, the resetTFTs, the buffer TFTs, and the selection TFTs generate an image signalfrom the light irradiated onto the photodiodes; the operation keys haveLEDs; and the direction of an image displayed by the LEDs is switchable.9. An electronic device functioning as a telephone, comprising: a firstpanel having: one of an audio input portion and an audio output portion;and a display portion; a second panel having: one of an audio inputportion and an audio output portion; and operation keys; wherein: thefirst panel and the second panel are connected; the angle between thefirst panel and the second panel can be arbitrarily changed; the displayportion has a plurality of pixels; the plurality of pixels each have: aphotodiode; an EL element; a switching TFT; an EL driver TFT; a resetTFT; a buffer TFT; and a selection TFT; the switching TFT and the ELdriver TFT control light emission from the EL element; light emittedfrom the EL elements is reflected upon a subject and irradiated onto thephotodiodes; the photodiodes, the reset TFTs, the buffer TFTs, and theselection TFTs generate an image signal from the light irradiated ontothe photodiodes; the operation keys have liquid crystals; and thedirection of an image displayed by the liquid crystals is switchable.10. An electronic device according to any of claims 1 to 9 , wherein:the EL elements each have an anode, a cathode, and an EL layer formedbetween the anode and the cathode; and the external quantum efficiencyof the EL layer is equal to or greater than 10%.
 11. An electronicdevice according to any of claims 1 to 10 , wherein the strength oflight emitted by the EL elements is equal to or greater than 251 m/W.12. An electronic device functioning as a telephone, comprising: adisplay portion; an audio input portion; an audio output portion; andoperation keys; wherein: the display portion have first EL elements; theoperation keys have second EL element; and the direction of an imagedisplayed by the second EL elements is switchable.
 13. An electronicdevice functioning as a telephone, comprising: a first panel having: oneof an audio input portion and an audio output portion; and a displayportion; a second panel having: one of an audio input portion and anaudio output portion; and operation keys; wherein: the first panel andthe second panel are connected; the angle between the first panel andthe second panel can be arbitrarily changed; the display portion hasfirst EL elements; the operation keys have second EL elements; and thedirection of an image displayed by second EL elements is switchable. 14.An electronic device functioning as a telephone, comprising: a firstpanel having: one of an audio input portion and an audio output portion;and a display portion; a second panel having: one of an audio inputportion and an audio output portion; and operation keys; wherein: thedisplay portion has first EL elements; the operation keys have second ELelements; the first panel and the second panel are connected; the anglebetween the first panel and the second panel can be arbitrarily changed;and the direction of an image displayed by second EL elements isswitchable in accordance with the angle between the first panel and thesecond panel.
 15. An electronic device functioning as a telephone,comprising: a first panel having: one of an audio input portion and anaudio output portion; and a display portion; a second panel having: oneof an audio input portion and an audio output portion; and operationkeys; wherein: the first panel and the second panel are connected; theangle between the first panel and the second panel can be arbitrarilychanged; the display portion has a plurality of pixels; the plurality ofpixels each have: a photodiode; a first EL element; a switching TFT; anEL driver TFT; a reset TFT; a buffer TFF; and a selection TFT; theswitching TFT and the EL driver TFT control light emission from thefirst EL element; light emitted from the first EL elements is reflectedupon a subject and irradiated onto the photodiodes; the photodiodes, thereset TFTs, the buffer TFTs, and the selection TFTs generate an imagesignal from the light irradiated onto the photodiodes; the operationkeys have second EL elements; and the direction of an image displayed bythe second EL elements is switchable.
 16. An electronic device accordingto any of claims 12 to 15 , wherein: the first EL elements each have ananode, a cathode, and an EL layer formed between the anode and thecathode; and the external quantum efficiency of the EL layer is equal toor greater than 10%.
 17. An electronic device according to any of claims12 to 16 , wherein the strength of light emitted by the first ELelements is equal to or greater than 251 m/W.
 18. An electronic deviceaccording to any of claims 12 to 17 , wherein: the second EL elementseach have an anode, a cathode, and an EL layer formed between the anodeand the cathode; and the external quantum efficiency of the EL layer isequal to or greater than 10%.
 19. An electronic device according to anyof claims 12 to 18 , wherein the maximum value of the strength of lightemitted by the second EL elements is equal to or greater than 251 m/W.20. An electronic device according to any of claims 1 to 19 , whereinthe electronic device has a CCD light receiving portion.
 21. Anelectronic device according to claim 20 , wherein an image is taken inas electronic date in the CCD light receiving portion.
 22. An electronicdevice according to any of claims 1 to 21 , wherein: the display portionhas a touch panel; and an image written into the touch panel is read inas electronic data.
 23. An electronic device functioning as a telephone,comprising: a first panel having: one of an audio input portion and anaudio output portion; and a display portion; a second panel having: oneof an audio input portion and an audio output portion; and operationkeys; wherein: the first panel and the second panel are connected; theangle between the first panel and the second panel can be arbitrarilychanged; the display portion has EL elements; the operation keys haveLEDs; the direction of an image displayed by the LEDs is switchable; andthe direction of an image displayed by the EL elements and that of theimage displayed by LEDs are the same at all times.
 24. An electronicdevice functioning as a telephone, comprising: a first panel having: oneof an audio input portion and an audio output portion; and a displayportion; a second panel having: one of an audio input portion and anaudio output portion; and operation keys; wherein: the first panel andthe second panel are connected; the angle between the first panel andthe second panel can be arbitrarily changed; the display portion has ELelements; the operation keys have liquid crystals; the direction of animage displayed by the liquid crystals is switchable; and the directionof an image displayed by the EL elements and that of the image displayedby liquid crystals are the same at all times.
 25. An electronic devicefunctioning as a telephone, comprising: a first panel having: one of anaudio input portion and an audio output portion; and a display portion;a second panel having: one of an audio input portion and an audio outputportion; and operation keys; wherein: the display portion has ELelements; the operation keys have LEDs; the first panel and the secondpanel are connected; the angle between the first panel and the secondpanel can be arbitrarily changed; the direction of an image displayed bythe LEDs is switchable in accordance with the angle between the firstpanel and the second panel; and the direction of an image displayed bythe EL elements and that of the image displayed by LEDs are the same atall times.
 26. An electronic device functioning as a telephone,comprising: a first panel having: one of an audio input portion and anaudio output portion; and a display portion; a second panel having: oneof an audio input portion and an audio output portion; and operationkeys; wherein: the display portion has EL elements; the operation keyshave liquid crystals; the first panel and the second panel areconnected; the angle between the first panel and the second panel can bearbitrarily changed; the direction of an image displayed by the liquidcrystals is switchable in accordance with the angle between the firstpanel and the second panel; and the direction of an image displayed bythe EL elements and that of the image displayed by liquid crystals arethe same at all times.
 27. An electronic device functioning as atelephone, comprising: a first panel having: one of an audio inputportion and an audio output portion; and a display portion; a secondpanel having: one of an audio input portion and an audio output portion;and operation keys; and a means of recognizing an angle between thefirst panel and the second panel, wherein: the display portion has ELelements; the operation keys have LEDs; the first panel and the secondpanel are connected; the angle between the first panel and the secondpanel can be arbitrarily changed; the direction of an image displayed bythe LEDs is switchable in accordance with the angle between the firstpanel and the second panel.
 28. An electronic device functioning as atelephone, comprising: a first panel having: one of an audio inputportion and an audio output portion; and a display portion; a secondpanel having: one of an audio input portion and an audio output portion;and operation keys; and a means of recognizing an angle between thefirst panel and the second panel, wherein: the display portion has ELelements; the operation keys have LEDs; the first panel and the secondpanel are connected; the angle between the first panel and the secondpanel can be arbitrarily changed; the direction of an image displayed bythe LEDs is switchable in accordance with the angle between the firstpanel and the second panel; and the direction of an image displayed bythe EL elements and that of the image displayed by LEDs are the same atall times.
 29. An electronic device functioning as a telephone,comprising: a first panel having: one of an audio input portion and anaudio output portion; and a display portion; a second panel having: oneof an audio input portion and an audio output portion; and operationkeys; and a means of recognizing an angle between the first panel andthe second panel, wherein: the display portion has EL elements; theoperation keys have liquid crystals; the first panel and the secondpanel are connected; the angle between the first panel and the secondpanel can be arbitrarily changed; the direction of an image displayed bythe liquid crystals is switchable in accordance with the angle betweenthe first panel and the second panel.
 30. An electronic devicefunctioning as a telephone, comprising: a first panel having: one of anaudio input portion and an audio output portion; and a display portion;a second panel having: one of an audio input portion and an audio outputportion; and operation keys; and a means of recognizing an angle betweenthe first panel and the second panel, wherein: the display portion hasEL elements; the operation keys have liquid crystals; the first paneland the second panel are connected; the angle between the first paneland the second panel can be arbitrarily changed; the direction of animage displayed by the liquid crystals is switchable in accordance withthe angle between the first panel and the second panel; and thedirection of an image displayed by the EL elements and that of the imagedisplayed by liquid crystals are the same at all times.